Popular Science Monthly/Volume 78/January 1911/The Smallest of the Century Plants

by William Trelease

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THE

POPULAR SCIENCE

MONTHLY

 

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JANUARY, 1911

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THE SMALLEST OF THE CENTURY PLANTS^[1]

By Professor WILLIAM TRELEASE

MISSOURI BOTANICAL GARDEN

SELECTION of these particular plants from the very large number that have occupied my attention for the last ten years is based on a recognition of the fact that it is extremes—the largest and smallest,

Fig. 1. About the Mediterranean

Fig. 2. Grown for Pulque.

the best and the worst—rather than ordinary or average things which attract human interest. The present very short communicaion may be called a vest-pocket account of the vest-pocket edition of the century plant. The use of this name, however, is not quite accurate, for the century plant properly is that large Agave, standing as the type of its genus, which was introduced into Europe not so very long after the discovery of the new world by Columbus, which has now become thoroughly naturalized about the Mediterranean, and which in northern

Fig. 3. Thick as a Man's Body.

countries, even when protected against the winter, literally takes the larger part of a century for its development. In the popular mind the idea of a century plant also includes the enormous species grown for pulque on the elevated plains to Fig. 4. Giants and Pygmies. the south of the City of Mexico, and even larger plants of the same type, each of them reaching the weight of a ton or more, and sometimes producing a flower stalk nearly as thick as a man's body. In this sense, then, the name century plant becomes nearly equivalent to the Haitian name maguey, as now applied in Mexico, where the Spaniards introduced it in place of the Aztec name for these plants—metl. My use of the word, then, is rather as an equivalent of the botanist's generic name. Agave, than of this particular designation of a part of its species.

A comparative notion of the size of these giants of the genus and its pygmies, with which I am here concerned, is afforded by a photograph of the latter, taken by the side of two of the fruiting branches of a mammoth West Indian species which I have hanging to a chimney breast in my study. Fig. 5. Scarcely equals a Seed Vessel. The larger of these dwarfs is no larger than one's fist, and the smaller scarcely equals the seed-vessel of a great maguey.

The larger of these species was first discovered by the international survey of the boundary between Arizona and Sonora, more than half a century ago, and although it is abundant on the ragged mountains of the boundary region, it has been collected very few times so far as yet known, since then: ten years ago near the one hundred and twenty-ninth boundary monument in the Pajarito Mountains by myself when I was looking up typical material of some of the species first made known through the International Boundary Survey; last year when

Fig. 6. In the Pajarito Mountains.

Mr. J. C. Blumer collected it in the same region; and this season when Mr. James H. Ferriss found it in the Guija Mountains. The little plant here illustrated is the one sent in by Mr. Blumer, which in transit had begun to develop a flower stem and which, flowering in May of last year and fruiting in the following summer, has given the first opportunity for a botanist to observe these phenomena and to see in perfection its diminutive flowers which, scarcely three quarters of an inch long, led its describer, Dr. Torrey, to name it Agave parviflora.

Like those of many agaves and yuccas and some other genera the solid stem and thick leaf bases of this plant contain a saponifying substance which has won for it, as for these various plants, the name amole, or soap-weed. Its thick, rounded leaves, like those of a comparatively few other species in the genus are beautifully marked by irregular stripes of pure white, due to bits of cuticle torn from other leaves as the central bud or cogollo opened. When Dr. Engelmann presented his classical notes on Agave to the academy thirty-five years ago, he stated that the occurrence on the margins of these leaves of detaching threads above and little prickles below was, so far as known, unique in the genus, and except for a very few close relatives of this plant the statement still holds true.

Fig. 7. Candelabrum-like Panicles.

The main kinds of Agave fall into two recognized classes: one, illustrated by the true century plant and the pulque magueys, bears flowers in candelabrum-like panicles; the other, like the lechuguilla, has its flowers disposed mostly in pairs along a wand-like spike. An effort has been made to separate these latter from Agave under the generic name Littæa, but this has not met with general acceptance and in fact there are puzzlingly intermediate species, as, for instance, the Littæa

Fig. 8. A Wand-like Spike.

characteristic of the Grand Cañon, and a garden Littæa which many years ago I named in commemoration of the accurate student of this group of plants, Engelmann.

Agave parviflora is clearly a Littæa, with its flowers rather loosely disposed along the upper part of an inflorescence wand scarcely thicker than a goose-quill, but its flowers by no means grow in pairs, though each short main stalk forks at the beginning. On the contrary, clusters of six or eight flowers—of which all but two or four commonly fail to develop—are borne by its forked primary branches, a study of which is capable of throwing much light on the reduced rather than primitive typical twin flowers of the littæas.

As with all of the agaves that have been studied so far, this species matures the stamens and pistils of a given flower at different times. The flowers, which open early in the morning, quickly protrude their stamens and shed their pollen immediately, but the style is then no

Fig. 9. Characteristic of the Grand Cañon.		Fig. 10. Agave parviflora.

Fig. 11. Early in the Morning.

Fig. 12. The next Morning.

longer than the perianth and its stigma is not receptive for pollen. By the next morning, however, the style has reached the stamen in length, though it is still unreceptive. After two days, the stamens have shriveled and drawn out of the way and the stigmatic lines have become fleecy and moist, indicating receptivity. Though scentless, and greenish white, rather than brightly colored, the flowers secrete an abundance of nectar which with the proterandry points to cross pollination by the aid of insects.

When Arthur Schott collected the type specimens of Agave parviflora it was in fruit, though the upper part of some of the specimens still retained a few unopened buds, and a few sterile, dried-up flowers were included in the collection. My own observation of the plant in the field was also made during its fruiting season and I am not aware that its fresh flowers have ever been seen except on this specimen. The main structural characters of the flowers were accurately made out by Engelmann and are preserved in his perfectly prepared dissections, but the contribution which this little specimen has made to a correct understanding of their shape and proportions is clearly shown by a comparison of these type flowers with its own.

Almost if not quite as small as Agave parviflora are two other species in many respects closely similar to it: a little plant found in northern Mexico on the Lumholtz expedition, which Mr. Watson named, after its discoverer. Agave Hartmani, and an unnamed plant of similar habit but with a short perianth tube equalled in length by the perianth lobes, which Professor Tourney found eighteen years ago in the Pinal Mountains of Arizona. In the course of my study of this group of agaves with thread-margined leaves I have also encountered a garden plant of about twice the dimensions of A. parviflora and with differently shaped leaves, which has been grown under the name of parviflora but which is not unlikely to prove more closely related to the thread-bearing amoles of central Mexico. The prickly margin and its replacement by detaching threads which characterize parviflora are particularly well shown on the juvenile foliage of offsets from this plant.

The other and still smaller dwarf first came into the market under the trade name Agave pumila—given because of its minute size—about thirty-five years ago, the earliest mention of it that I find being in a catalogue published in 1877. No record is available as to the source of the plants then or now in commerce, though I have been told that a collector of such plants has seen it in the Andes of Colombia. Like many other agaves, this produces offsets freely and is now rather extensively cultivated. It was named in 1888 by Mr. Baker, who stated that his plant—about as large as the one here shown—had not increased appreciably in size for the eight years during which it had been cultivated at Kew. Though I have no doubt that it grows to something more than this walnut-size, I shall be surprised if it ever reaches the proportions of parviflora. It is known in botanical literature only from the original description. Its very thick leaves have short, sharp end-spines, decurrent on the margin in a dried line of the same texture as the little marginal prickles. From the fact that this margin was not continuous, Mr. Baker was led to range Agave pumila in his submarginate

Fig. 13. Juvenile Foliage.	Fig. 14. Lined with Dark Green.

series, which brings this, the least of all agaves, close beside the greatest of its congeners, the gigantic Fig. 15. The Lechuguilla. pulque magueys. It would be surprising if, when its flowering is made known, pumila were found to develop a diminutive candelabrum inflorescence; in fact, this is not to be expected. A character shown by this specimen and, so far as I know, never before noted publicly, is that the backs of its leaves are finely lined with dark green on a lighter background. Though generalizations are unsafe, I may say that in the course of an exhaustive study of all of the agaves that it has come my way to see I have thus far seen such lining only on littæas of the horny-margined section, like the lechuguilla—the marking being due, in fact, to the development of what may be called an emergency water tissue on the lower side of the leaves, the darker green stripes marking points at which the full chlorophyll-bearing tissue comes out to the epidermis and the water tissues developing more or less chlorophyll according to differing conditions of drought and exposure to light. There is every reason to believe, therefore, that when it flowers Agave pumila will produce a littæa spike and flowers similar to, if not so large as, those of A. lecheguilla.

No agaves are known south of the isthmus of Panama except one of the West Indian panicled series which has developed in the Venezuelan coast region, and a little-known plant of the Andes, near Lima, which is evidently a littæa, though of a mezcal series, quite unrelated to the horny margined group. It need, therefore, be little more surprising if Agave pumila of the latter group is found to be really at home in the Andes, than that another littæa type should be found in the same exile, though relatives of the latter are characteristic of southern Mexico while known marginate specie? are more northern.

1. A lecture before the Academy of Science of St. Louis, delivered October 17, 1910.