Page:Bulletin of the Torrey Botanical Club 30 214-224.djvu/9

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Howe and Underwood: The Genus Riella

barium of the New York Botanical Garden. The plants are said by Professor Earle to have been found in a pool headed by a small waterfall, forming mats on rocks and stones which were covered by 10–60 cm. of water in the dry season. The same species was collected by Schott in 1855, his specimen originating from "Limpia, near its head, Western Texas." His plants, though otherwise agreeing perfectly with those of the more recent collection, are considerably smaller and are mostly unbranched. A Riella (in herb. A. W. Evans) was collected by Mr. De Alton Saunders at Brookings, South Dakota, in 1898. The material is scanty and the sporogonia are so immature that the spore-characters cannot be determined. The involucres and scales are similar to those of R. Americana and it is quite probable that the species is the same. This South Dakota specimen marks the northern limit in the known distribution of the genus.

Riella Americana is easily distinguished from any of the species hitherto known. Its nearest ally is probably Riella Battandieri f. Gallica, of southern France, which differs in being monoicous,[1] in the narrower wing, the smaller spores, with shorter non-capitate spines, etc. Gemmae have not before, to our knowledge, been definitely described in any species of Riella, though Goebel (Flora, 77: 105. 1893) in figuring three young stages of Riella Battandieri (?) remarks in a footnote that one of them sprang from a "Zellkörper" while the others came from "Zellfäden." By analogy with what we have observed in Riella Americana, it seems very probable that his plant from the "Zellkörper" came from a brood-body of some kind, while those from the "Zellfäden" were derived from spores. The young plants of Riella Cossoniana, represented by Trabut in his figures 1 and 2 (l. c.), also, with little doubt, originated from gemmae. The gemmiform appendages figured by Trabut on the axis of his R. Gallica are of a more doubtful nature. These were not found by Corbière in his recent studies of what he believes to be the same species; possibly they were designed to represent remains of old involucres and sporogonia.

The gemmae of R. Americana originate on the axis as trichomic outgrowths, each of about three cells in a single series (f. 10, 11) of which the terminal cell is usually the largest. The two

  1. Corbière, Rev. Bryol. 29: 111, 113. 1902.