142 Johnson— Observations on Phaeozoosporeae . 
5. Desmarestia Lamour. 
Trichothallic growth . In this abundant and widely-distri- 
buted genus the mode of growth of the thallus is readily 
observable (Fig. 12). It has been described in detail by 
Janczewski 1 , and later by Falkenberg 2 . The thallus is 
pinnately branched, the main stem and all its branches end, 
when in the growing condition, in an uniseriate septate hair 
possessed of basal growth. This primary filamentous axis 
persists as such, and is recognisable in the thickest part 
(J inch or more) of the thallus. The axial hair is itself 
abundantly branched in a pinnate manner in its uncortexed 
part. It is from the basal cells of its pinnules, on the thallus 
side of its merismatic region, that the whole of the extensive 
cortex is primarily derived. It will be seen how this mode of 
growth in Desmarestia , like that in the Tilopterideae, is but 
a complication of that in Ectocarpus Lyngb. 
Reproductive organs. Though the genus Desmarestia is so 
widely distributed and of great systematic importance, the 
only description of the sporangia is the very brief one by 
Thuret and Bornet 3 : ‘ Je rappellerai que dans le Desmarestia , 
ou du moins dans le D. viridis , car dans le D. Dudresnayi 
Lamx. 4 , MM. Crouan (Florule du Finistere, Tab. 30) figurent 
une forme de fructification tres difierente, les sporanges se 
forment egalement dans les cellules corticales. Mais les 
cellules fructiferes ne presentent aucune modification de forme 
et de dimension et ne se distinguent des cellules corticales 
ordinaires que par la nature de leur contenu/ I was successful 
in finding D. ligulata in a fertile state. The sporangia are, as in 
D. viridis , unilocular, and, as in it, are only to be distinguished 
from ordinary cells by the nature of their contents (Figs. 12, 
13). In D. ligulata , however, the sporangia are not confined 
1 Janczewski, op. cit. p. 106. 2 Falkenberg, op. cit. p. 221, Fig. v. 
3 Thuret et Bornet, Et. Phyc. p. 16. 
4 The figure referred to in MM. Crouan’s Florule (Tab. 30. 1 91 , Fig. 3) is ‘ ramule 
de Desm. viridis avec un sporange disseminant ses sporidies.’ It is an incomplete 
figure representing apparently the escape of numerous spores from a unilocular 
sporangium. 
