Timherlake — Swarm-Spores of Hydrodidyon. 511 



come to rest, lose their cilia, become surrounded by cellulose 

 walls, and become attached to one another at various points so 

 as to form a young net that is later set free by the breaking 

 down of the mother cell wall. The changes that occur in the 

 cell contents during growth are of importance as throwing 

 some light upon the structures found in mature cells. In the 

 very young cells I have looked carefully for the first indica- 

 tions of the formation of the pyrenoids but without getting 

 much light as to the nature of the process. As Braun long 

 ago showed, these organs are formed shortly after the spores 

 come to rest. The youngest stages in which I could clearly 

 distinguish structures that were undoubted pyrenoids showed 

 them as small spherical red stained bodies enclosed by a hya- 

 line region sharply bounded off from the surrounding cyto- 

 plasm (Figs. 41 and 42). The difiiculty of identifying the 

 earliest sta£:es in the formation of such structure lies in the 

 fact that any of the numerous granules so frequently found in 

 the cell may be mistaken for a young pj^renoid, and I have not 

 discovered any reaction by which to determine whether such 

 bodies are or are not the young pyrenoids. It is interesting, 

 however, in this connection, to note that the pyrenoids and nu- 

 clei are generally quite closely associated in the young cells, 

 and that in manv cases tlie number of nuclei is the same as 

 that of the pyrenoids. But this equality is lost in the older 

 stages and the number of nuclei is frequently in excess of the 

 number of pyrenoids. The reverse condition, however, is 

 often observed. See especially Fig. 44, where the number of 

 pyrenoids is greatly in excess of the number of nuclei, a rela- 

 tion that holds quite generally in the case of these very large 

 nuclei. 



I did not find any stages of the first nuclear division, but a 

 comparison of Figs. 40 and 41 shows clearly that a large in- 

 crease in the size of the cell may occur before any nuclear 

 divisions take place. (See also Fig. 43.) It is important to 

 note, however, that the increase in size of the cell is out of 

 proportion to the increase in the amount of protoplasm. 

 Before a cell has grown very much, fairly large vacuoles begin 

 to appear in either end apparently leaving a very thin layer of 



