2 20 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



cells are better off as gonidia than as independent algae. 



The next difference to be noted between the invested and 

 uninvested gonidia is in their subsequent behavior in culture. 

 Within a very few days (at the utmost six) the gonidia 

 which contain haustoria, or which have hyphal fragments 

 still attached to them, have either divided by internal cell- 

 division at least once, or their cell-contents have contracted 

 away from the wall. Figures 6, 7, 8, 9 show various stages 

 in the division of invested gonidia, in fig. 6 into two, in 

 fig. 7 into four, in fig. 8 another divided into four, in fig. 9 

 at a the same cell twenty-four hours after, when the wall of 

 the mother-cell had become dissolved, setting free eight 

 daughter-cells. In fig. 9 at the *, and in fig. 10, we have 

 gonidial cells in which the haustoria, broken away from the 

 hyphse which formed and bore them, are plainly visible, the 

 contents of the gonidial cells contracting away from, and in 

 in this way escaping, the haustoria. Later the contracted 

 mass surrounds itself by a new wall and behaves like the 

 uninvested gonidia. These last do not divide in the culture 

 for a very long time. 



The only difference between the invested and unin- 

 vested gonidia in the culture being in their relation to an 

 organism incapable of manufacturing its own food, it can 

 be safely concluded that the cell-contents of the former 

 divide, or contract away from the wall, in order to eliminate 

 the foreign organism, and to produce individuals which 

 will be free from it. The conditions prevailing in a hang- 

 ing-drop culture cannot be entirely favorable to the green 

 cells; if they were, all the gonidial cells would sooner or 

 later divide. Haustoria within, or hyphal branches closely 

 enwrapping them, must irritate the invested gonidia. The 

 response to this irritation is an effort to get rid of it by 

 contraction or by division. The uninvested gonidia, not 

 subjected to this irritation, do not contract or divide. 



The gonidia of R. reticulata are in rounded masses fairly 

 compact and held together by hyphas (figs. 5 and 11, 

 and Peirce [1898], p. 412). Many of these masses are 

 composed of small cells, and some of the cells are likely 



