﻿Evans: The genus Plagiochasma 271 



of the carpocephalum a circle of slender scales (see Figs. 4, E; 

 5, E-G; etc.) makes its appearance very early; these scales, 

 according to Leitgeb (18, p. 67), are in two series and they show 

 the same purple pigmentation as the androecial scales, becoming 

 bleached out with age. When the capsules have reached maturity 

 the region between the carpocephalum and the thallus undergoes 

 intercalary growth and elongates into a stalk, some of the scales 

 remaining at the base and some being carried up with the carpo- 

 cephalum. The length of the stalk varies greatly in different 

 species and even in the same species under different conditions. 

 Sometimes it is so short that it scarcely raises the carpocephalum 

 above the thallus. The stalk is remarkable on account of the 

 fact that it possesses no rhizoid-furrow, although it may be ir- 

 regularly grooved. 



With regard to the morphology of the carpocephalum in 

 Plagiochasma and in Clevea, where similar conditions obtain, the 

 opinions of writers vary. Leitgeb (18, p. 29) considered the whole 

 structure a highly developed dorsal outgrowth of the thallus, 

 comparable with the low outgrowths found in Corsinia. He based 

 his conception on the continued growth of the thallus after the 

 initiation of the carpocephalum and on the lack of a rhizoid- 

 furrow in the stalk, both indicating that the growing point of the 

 thallus was not involved. He therefore considered that the carpo- 

 cephalum in these two genera was morphologically different from 

 the very similar carpocephalum found in Rehoulia, Sauieria, and 

 more complex forms, where the initiation of the carpocephalum 

 brought the growth of the thallus to an end and where the stalk 

 showed one or tw^o rhizoid-furrows. In these cases he considered 

 that the carpocephalum represented a modified shoot (or shoot- 

 system) in which the growing point of the thallus was directly 

 involved. Leitgeb's views regarding the androecium were very 

 similar. Not only in Plagiochasma but also in Reboulia and other 

 genera, where the development of the androecium failed to stop 

 the growth of the thallus, he considered the structure a mere 

 dorsal outgrowth and therefore morphologically different from 

 the androecium in Preissia and related genera, where it represented 

 a modified shoot. 



Goebel (8, p. 46) has recently pointed out that these ideas 



