158 University of California Puhlicaiions. [botany 



shape, size and interspaces, and also an outer gelatinous 

 envelope of about the ordinary thickness. 



Of course there are some alterations in the form and structure 

 of the alga; but this always occurs where a parasite takes com- 

 plete possession of its host and penetrates all its tissues. Under 

 such conditions the alga could not develop normally in every 

 detail. Consequently there is a general thickening of the frond, 

 a deeper coloration, a greater irregularity in shape and surface 

 of frond, with leathery texture, and also less regular and nar- 

 rower cells. 



All these changes would naturally result from the growth 

 and development of the mycelium between the cells and in the 

 medulla. The development of the perithecia completes the 

 abnormal growth and change in the form of the frond, by 

 causing the numerous swellings and openings into the medulla. 

 Perhaps instead of being a symbiotic relation, where each is 

 benefited, it may l)e a case of extreme parasitism, where the 

 ascomycete is the aggressor and receives all the benefit at the 

 expense of the alga. In none of the material examined has any 

 alga been found fruiting or showing any signs of fruit. Probably 

 it has not vitality enough to support the funguS/ and also fruit. 

 Yet the plant continues comparatively abundant and persistsnt 

 throughout the year. The ascomycete on the contrary continues 

 producing ascospores throughout the year with undiminished 

 vigor and abundance. The fungus is evidently favorabl}^ situated 

 for growth and reproduction. 



It may be after all that the relation of these two plants is 

 symbiotic, and they may be mutually benefited by the union, 

 though there is no doubt that the fungus receives the most, 

 because it cannot exist without a chlorophyllose plant to produce 

 its food, while the alga is able to get its nourishment dire(!tly 

 from inorganic material. It furnishes not only food but also 

 protection to the ascomycete. Possibly the mycelium of the 

 ascomycete toughens and holds the frond together so that it can 

 better resist wind and weather. It is certainly much tougher 

 and better able to resist the waves than an ordinary Ulva. 



In the Prasiola-composite the relation of the fungus to the 

 Prasiola is probably much the same as that of the Ulva, though 



