Evans: HEpATICAE oF PuEeRTo Rico 507 
Puerto Rico Leptolejeuneae exhibit a vegetative reproduction by 
means of leafy propagula. These arise just behind the leaves in 
the position usually occupied by normal branches. They are to be 
looked upon, therefore, as modified branches, the whole of the 
branch, with the exception of the basal sheath, taking part in the 
formation of the propagulum. Leafy propagula have already been 
noted in Plagiochila and in various other genera of the Jun- 
germanniceae, but in all cases which have been described they 
have arisen directly from leaf-cells or more rarely from indefinitely 
situated axis-cells. Goebel * ascribes the formation of these pro- 
pagula to the latent power retained by every cell of the liverwort 
(. ¢., of the gametophyte) to develop as if it were a spore—a 
power which is not made manifest until the plant becomes en- 
feebled. Propagula of this character are essentially different from 
those of Lepfolejyeunea, in which the reproductive bodies represent 
entire branches. The latter, although described for various mosses, + 
have not before been recorded for any of the leafy hepatics. 
The modifications in structure which are exhibited by the pro- 
pagula of Lepfolejeunea are in part explicable by their function as 
reproductive bodies and in part by the peculiar habitat of the 
Species, namely the smooth and glossy surface of evergreen leaves. 
These modifications are most pronounced in L. exocellata and L. 
elliptica, and the propagula of these two species, which are essen- 
tially alike, will be considered first. Instead of spreading widely 
as it would if it were a normal branch, a young propagulum grows 
toward the apex of the stem, lying above the leaves and parallel 
with the axis or only slightly diverging from it (f/. 23, f. 9). In 
assuming this position its axis curves abruptly near the base in 
such a way that the antical surface of the propagulum is turned 
downward, while the postical surface with its underleaves is turned 
upward. 
The first few leaves and underleaves of the propagulum (f. 70) 
are very different from those borne on ordinary axes. The leaves, 
although larger than the first leaves of a normal branch, are 
Shorter than typical leaves and are nearly as broad as long. Their 
* Organographie der Pflanzen, 277. 1898. 
TCf. Correns. Unters. iiber die Vermehrung der Laubmoose durch Brutorgane und 
Stecklinge, 1899. £. ¢., Plagiothecium elegans, p. 250. 
