152 Universiti/ of California PuhUcaiions. (botany 



and less abiiiidaiit in the younger plants. Sections were made of 

 fronds in all stages of combination, from those without any or 

 very few hyphal threads, to those completely penetrated with a 

 closely interwoven mycelium. (Of. Figs. 8-12, PI. 16.) 



The young fronds, scarcely infected with the fungi, are 

 monostromatic, but the older composites are from eight to six- 

 teen cells thick. This gradual increase in the number of cells 

 and consequently of the thickness of the fronds is shown in the 

 series of sections represented in figures 8 to 12 on i)la.te 16. 

 Soon after the fungus takes possession of the frond, the cells 

 begin to show the same tetrad arrangement in the cross section 

 as seen from the surface, there being one, two, three or four 

 tetrads in the cross section of the oldest fronds. Each tetrad is 

 closely surrounded by the interwoven mycelium which forms a 

 kind of capsule. In the monostromatic stage the cells are oblong 

 to oval or elliptical and often columnar like the palisade cells of 

 the higher plants. After the first division, which is always 

 transverse to the cell, the cells become quadrangular and alw^ays 

 remain so in the later stages. The tetrads are less regular in 

 shape, size, and arrangement near the perithecia, and often are 

 separate or broken up into two or even into single cells more or 

 less flattened. In the early monostromatic stage the cells are 

 11-14 /A in vertical diameter and 3-9 /* in horizontal diameter; 

 while in the later mature stage of the composite the cells are 

 5-11 /A square. The immature or monostromatic fronds are 

 16-45 jtA thick, while the mature fronds are 75-146 /* thick. 



The hyphte which invest the algal cells, and are interwoven 

 in all directions around the tetrads are very coarse, somewhat 

 angular, with very thick walls and small lumen. They vary from 

 1.5 to 3 /A in diameter at the tips. The inner hyph^e are 

 finer, about 1 /* in diameter and colorless, but the lateral 

 branches, projecting out into the cortex, are slightly enlarged, 

 becoming club shaped and also slightly pigmented, especially at 

 the extreme tips around the perithecia and on the surface of the 

 frond. They stand out vertically, embedded just beneath the 

 outermost gelatinous layer. The hyph« do not enter the algal 

 cells, but simply lie close to their walls completely surrounding 

 them, forming a sort of capsule about each tetrad when the frond 

 is mature. 



