162 MINNESOTA BOTANICAL STUDIES. 



have the appearance characteristic of the cystocarp region. A 

 comparison with figures in which trichogynes are represented 

 shows but slight similarity in appearance. The pericarp consists 

 of the two layers found in the lamina and stipe. The outer small 

 cells containing chromatophores pass somewhat abruptly to the 

 cells of the interior (Fig. 21, PL 14), which are elongated and 

 connected to form a more or less dense net-work. In most cases 

 the transverse connecting cells are more numerous than in Fig. 

 21, so that the pericarp presents the reticulated appearance of 

 the tissue in Fig. 19. Very frequently, however, the cells show 

 much lateral crowding in the pericarp. 



The cystocarp is compound and the spores are aggregated 

 into distinct groups (Fig. 19, PI. 14). This is clearly seen in 

 all but the oldest cystocarps and even here a carefully cut sec- 

 tion shows it. These groups are separated from each other by 

 large, empty cells, with smaller cells of the same character ex- 

 tending between them (Fig. 20, PI. 14). This is brought out 

 very clearly by staining the section with iodine and then wash- 

 ing in water. 



The carpospores are more or less oval in shape, often some- 

 what angular. They measure from 12 to 15 mic. along one 

 diameter by 10 to 12 mic. along the other. 



The normal cystocarps measure from i to 2 mm. in diameter, 

 but it was noticed that frequently some were met with from two 

 to three times as large as the ordinary ones, measuring 2.5 to 

 3.5 mm. On examination it was discovered that the fronds of 

 another small alga were always found upon these large cysto- 

 carps. Several specimens were studied and it was found that 

 there was evidently more than one species infecting them. The 

 largest one discovered is represented in Fig. 7 a, PI. 13. It ap- 

 pears to emerge directly from the apical depression of the cys- 

 tocarp. A longitudinal section through the cystocarp shows 

 the parasite or epiphyte to consist of an axial cylinder of large 

 cells with protoplasmic connections between adjacent walls. 

 Most externally is a region of quadrilateral cells larger than the 

 corresponding cells of the host arranged quite irregularly, and be- 

 tween this and the central cylinder a region of long filamentous 

 cells, and it is these which are seen to penetrate the pith of the 

 pericarp (Fig. 22, PI. 14). They can be traced to the central 

 spore-bearing area, where they apparently curve outward and 

 follow along the side a short distance. They are distinguish- 



