92 WILLIAM TRELEASE ON THE 



and petioles are piiberuleiit or loosely villous, and the leaflets are occasionally somewhat 

 hairy. It should be noted that our flowers of this species and O. latifoUa are much 

 larger than those figured by Kunth. — PI. 11, fig. 14. 



A comparative biological study of the species of this genus, with abundant material, 

 would be of unusual interest. Those like O. corniculata, var. stricta, which produce 

 leafy stems, but spread by subterranean shoots, show how the caulescent type may be 

 connected with the acaulescent, as represented by the acetosella group, which produce 

 their leaves and flowers from the apex of a slender rhizome. These forest-inhabiting 

 species, with persistent stipular-dilated leaf-bases aggregated about the terminus of each 

 year's growth, wliile the scales are remote elsewhere, pave the way for the violacea group, 

 many of which are prairie or desert species. In some tropical American species of this 

 group, the so-called stipe, rising to the surface of the ground, is sparingly scaly, sug- 

 gesting the rhizome of 0. acetosella, while the subterranean part of O. enneaphylla 

 mi^ht be called with almost equal propriety a stout scaly intei-rupted rhizome, or a 

 closely aggregated series of bulbs. But, in the majority of these species, vegetative 

 propagation is effected by bulbiferous shoots, the bases of which disappear after a time, 

 while the inner leaf-bases persist at the apex as fleshy reservoirs of food, and the outer 

 scales, at length dry and sclerotic, usually villous-ciliate or quite hairy, sparingly 

 glandular and charged with resiu-cells, serve as protecting organs. The earliest vege- 

 tative energy of these bulbiferous plants in early spring goes to the expansion of foli- 

 age and flowers, but is soon diverted to the foi-mation of a fleshy tap root, rich in water 

 which is drawn iipon as the season of abundant moisture is succeeded by the drought of 

 summer, so that plants that grow in exposed districts are able to mature their fruit, 

 Avhile those in the woods frequently bloom through the late summer and autumn, hong after 

 their leaves have disappeared; finally the remaining store of water is applied to the 

 ripening of the bulb. 



Hildebrand,^ who has considered this subject at length, notes, apparently with reason, 

 that African species, which are exposed to greater heat during the dormant season than 

 those of America, uniformly produce bulbs that are protected by a thicker scaly coating, 

 while, by the greater length of their subterranean shoots, they are carried deeper into 

 the earth. The enlargement of the apices of these shoots with an accompanying reduc- 

 tion of their scales, or of the apices of slender rhizomes like those of 0. corniculata, var. 

 stricta, results in tubers such as characterize 0. crassicaulis^ and other species, several 

 of which bear large and edible tubers. 



While these cases may serve to illustrate the modification of the simple caulescent 

 type in one direction, O. Wriglitii departs from the corniculata type in developing a 

 stout subterranean caudex, from the summit of which the leafy branches spring, and this 

 form is much intensified in a group of acaulescent South American species with thick 



' Schutzeinriclitungen bei don Oxaliszwiebelii (Ber. ' Ziiccarini : Nachtrag Monogr. Ainer. Oxalisarten, 



deutscli. hot. Gessellsch., ir, 108) ; LebeusivciiiaUuisse dei' PI. 2. 



Oxalisarten, Jeiia, 1884,— abstract in Bot. Ceutralbl., xix, 



