500 
There is still another adaptive structural feature in the thallus 
of many lichens, especially in the Stictei, which is of undoubted 
physiological importance. These lichens present a striking ap- 
pearance by the numerous ridges and depressions on the upper 
surface of the thallus. Morphologically and physiologically the 
ridges are analagous to the vascular system in the true foliage 
leaves. On microscopic examination it is found that the majority 
of the medullary hyphae of the ridges extend parallel to the direc- 
tion of the ridges. In this region the medullary layer is also con- 
siderably thickened. It is a structure specialized to conduct the 
products of assimilation. This wavy outline of the thallus also 
increases surface expansion, whereby assimilation is increased. 
Assimilation is most active in the depressed portions of the thallus, 
which also corresponds to the position of the cyphellae on the 
lower surface. Such a wavy arrangement of structures also serves 
a mechanical function; according to the principles of mechanics 
it affords a better support to the frequently very large thallus. 
A Study of the Genus Galactia in North America. 
By ANNA MuRRAY VAIL. 
The genus Ga/actia was established by Patrick Browne in Nat. 
Hist. Jamaica, 298. p/. 32. f. 2. 1756. It was based on the plant 
figured in the illustration, a species with the stamens of Galactia 
and the showy scarlet flowers of Co//aea, which forms a connect- 
ing link between these two sections. Linnzus reduced the genus 
to Clitoria, describing the Jamaica plant under the name of C7itoria 
Galactia** Michaux in Fl. Bor. Am. 2: 61, revived the genus, 
with two North American species. 
The following genera have been reduced to Galactia: 
Odonta Bertol. Lucub. Herb. 35. 1822. 
Sweetta DC. Mem. Leg. 358. 1823. 
* The synonymy of this species is as follows: 
Gavactia Gatactia (L.). 
Clitoria Galactia L. Sp. Pl. Ed. 2, 1026. 1763. 
Galactia pendula Pers. Syn. 2: 302. 1807. 
Ittusr. Lindl. Bot. Reg. fi. 269. 1818. 
