Page:The American Cyclopædia (1879) Volume XII.djvu/686

672 ORCHIDS fringed ; in others it has its edges turned in to form a sort of tube, or it may be, as in the cypripediums (see LADY'S SLIPPER), distended to form a large inflated sac. It is upon the lip that the most beautiful colors and the strong- est markings are displayed, and not only on this account but by its greater size the lip is the most noticeable part of the flower. The base of the lip is frequently hollowed out to form a sac, or is prolonged to form a spur which secretes honey ; this in the greater green orchis is very long and conspicuous, it being the club-shaped body (4), nearly twice as long as the lip. In the centre of the flower are the reproductive organs, which in this family consist of one, or at most two stamens, united with the pistil, or rather the style ; the two being blended into a column makes the structure at first sight puzzling. In fig. 1 the column (5) is seen in the centre of the flower, and at 6 it is shown more enlarged ; it consists of a large anther united with a concave stigma seen between its widely separated cells. In the majority of the orchids the pollen is ag- glomerated in two or more pollen masses (pol- linia), in which the grains are held together by minute elastic threads, or are in a compact waxy mass ; these pollen masses (7), which are lodged in the cells or pockets of the anther, have often a little pedicel or stalk, at the base of which is a viscid disk or gland (8) ; this, com- ing in contact with an insect visiting the flow- er, adheres to it, and the pollen mass is thus withdrawn from its pouch and carried by the insect to another flower ; indeed, the structure is such throughout the whole family, varied admirably in different genera, that the flow- ers cannot be fertilized except through the aid of insects. As early as 1793 Sprengel showed that the pollen masses in some orchids could only be removed from their lodgment in the pouches by the aid of insects; and Robert Brown in 1833 announced the opinion that in- sects were essential to the fructification of most orchids. It remained for Darwin (" Fer- tilization of Orchids," London, 1862) to pre- sent the subject in all its details, to show the wonderfully varied mechanism of the different genera, and to point out the ben- eficial results from the intercrossing at- tending this method of fertilization. The relations of our na- tive orchids to in- sects have been stud- ied by Gray and oth- ers, and similar ob- FIG 2. Pollen Mass: or, justde- "*" *"*'-* npon plants. (See INSECT FERTILIZATION.) In flow- ers having a structure similar to that of the greater green orchis the act of fertilization is very simple, and may be imitated by the use of a lead pencil or similar pointed im- plement. The disk at the lower end of the pollen masses is so exceedingly viscid that when the pencil is thrust into the throat of the flower and withdrawn, like an insect's proboscis, one or both of the pollen masses are brought out with it; the viscid matter quickly hardening and fixing them firmly, as at #, fig. 2. If the pencil were now thrust into the throat of another flower, the pollen mass would not come in contact with the stigma, a difficulty which is overcome in a most won- derful manner. The stem of the pollen mass is endowed with a remarkable power of con- traction, and in about 30 seconds after its dis- lodgment from the anther cell the pollen mass assumes the position shown at &, always bend- ing toward the point of the pencil or the pro- boscis of the insect ; so by the time an insect, with the pollen mass glued to his head or probos- cis, can fly to another plant, the mass is in just the position to reach the stigma while the insect is searching for honey. In the greater green orchis, the tube containing the honey is so very long that but few insects have a proboscis sufficient to reach it, and it is thought by Gray that the work of fertiliza- tion is done by some of the sphinxes, which have been caught with pollen masses attached to their eyes, as in figs. 3 and 4, from Gray. Fig. 3 gives a side view of the head of the moth as it leaves a flower with the pollinia freshly at- tached to its eyes, and fig. 4 is a front view of the same head by the time it has reached an- other plant, the masses having assumed by curving a position which will bring them in contact with the stigma of the next flower the insect explores. The form and position of the Fie. 3. Head of Sphinx with recently attached Pollen Masses. FIG. 4. Head of Sphinx with Pollen Masses deflexed. pollen masses in other genera, and the mecha- nism of the operation, differ widely from the simple illustrations here given ; for these the reader is referred to Darwin's work. This