Olson : OBSERVATIONS ON GIGARTINA. 163 



able from the granular cells of the pericarp by their clear ap- 

 pearance. 



In most cases the infecting plant was found to be a smaller 

 one, represented in b Fig. 7, PL 13. It consists of simple or 

 branched filaments of oblong cells, but its entrance into the tis- 

 sues of the pericarp could not be detected. Its presence is evi- 

 dently the cause of the enlargement of the cystocarp, however. 

 Except in cases where the parasite can be seen within the tis- 

 sues of the cystocarp no difference except size can be observed 

 between the infested organs and the normal ones. 



Nemathecia. These were found upon only one frond in the 

 alcoholic material at command, but in this they were abundantly 

 distributed on both sides of the frond. They appear in surface 

 view as wart-like projections which can be distinguished with 

 the naked eye by their slightly lighter color (Fig. 8, PI. 13). 

 (It must be remembered that this description applies to alcoholic 

 material.) 



A section of the frond shows many interesting features. The 

 filaments of the internal pith area are even more loosely anas- 

 tomosed than in the vegetative part of the frond and show large 

 intercellular spaces. In this central area large, dark bodies the 

 size of spores were discovered scattered very abundantly among 

 the filaments (Fig. 24 e, PI. 14). These could easily be seen 

 from the surface, showing through the external area of cortex 

 cells, and even appear to the naked eye as tiny black dots. 

 Upon examination they were found to be of a dark green color 

 and apparently unicellular. They are evidently internal para- 

 sites, but no connection between them and the nemathecia could 

 be discovered, though it was earnestly sought, inasmuch as 

 Schmitz, in his article "Die Gattung Actinococcus Kutz,"* 

 ascribes the nemathecia of Phyllo-phora brodi&i and P. inter- 

 rupta to the parasite Actinococcus. 



Outside the central filaments is an area of approximately 

 spherical cells, which decrease gradually in size toward the ex- 

 terior. They exhibit a characteristic arrangement, i. e., from a 

 single basal cell two and sometimes three rows diverge toward 

 the surface. The outer layer is covered by a thick gelatinous 

 cuticle (Fig. 24, PI. 14). The tetraspores are evidently pro- 

 duced from the cells just outside the central filaments and are 

 formed in irregular masses just below the surface. 



* Schmitz. Flora. 77 : 367. 1893. 



