312 EVANS. 



In the early stages of germination the young plant simply repeats 

 the features of the gemma and develops into a narrow strap-shaped 

 thallus, strongly convex and bearing single or twinned hairs between 

 every two marginal cells (Fig. 9, D). As the growth goes on the 

 hairs of the gemma elongate and tend to equal those of the young 

 plant. Even this early stage may be long-continued, and repeated 

 dichotomies may take place before signs of further differentiation 

 become apparent. The plant may, in fact, become gemmiparous 

 almost immediately, and, in extreme cases, a gemma may form second- 

 ary gemmae before becoming detached. If differentiation proceeds 

 normally the young plant gradually grows wider, develops a costa, 

 and eventually shows the characteristic vegetative features of the 

 species. 



If the description just given is compared with the writer's earlier 

 description of the gemmae and gemmiparous branches in M . fndiculosa, 

 it will be seen that they correspond in most essential respects, and even 

 in their vegetative features the two species are strikingly alike. In 

 M. fndiculosa, however, the costa rather frequently shows three or 

 four rows of ventral cortical cells, the gemmiparous branches some- 

 times lose their wings completely (becoming radial in character), and 

 the gemmae are either plane or only slightly convex. In M. violacea, 

 on the other hand, the costa of a vegetative thallus rarely shows more 

 than two rows of ventral cortical cells (except just behind a dicho- 

 tomy), the gemmiparous branches apparently never lose their wings 

 completely (thus remaining dorsi ventral), and the gemmae are dis- 

 tinctly convex. On the basis of these slight differences and the wide 

 geographical separation of M. frutiadosa and M. violacea, it seems 

 justifiable to admit the validity of both, at least provisionally. 



Among the Chilean species M. violacea finds its closest allies in 

 M. decipicns, which never produces gemmae, and M. epiphyUa, which 

 produces marginal and submarginal gemmae on specialized branches. 

 The latter species is especially close, and the characters derived from 

 the costa, the alar cells and the hairs are almost identical, except that 

 the cell-measurements are a trifle higher. The following differential 

 characters, however, suffice to distinguish the species under most cir- 

 cumstances. In M. violacea the plants usually grow on wood and 

 develop a bluish coloration after being dried; the thallus is frequently 

 convex; the gemmiparous branches reach a high stage of specializa- 

 tion, giving off gemmae from the cortical cells of the costa as well as 

 from the alar cells ; and the gemmae themselves are distinctly convex. 

 In M. rpiphijlla the plants. usually grow on leaves and do not develop a 



