33 



filled by a homogeneous plasma, in which large amounts of starch 

 granules and fat drops develop, while a finely granular plasma col- 

 lects at the apex. The ovular membrane becomes extremely delicate 

 at the vertex, and at the time of fertilization softens to a jelly, or even 

 disappears entirely. 



The cells of the coronula form a tightly closed cap over the cap- 

 sule ; externally the ends of the enveloping cells are firmly united 

 over the ovule, but internally they are rounded off so that they rest 

 loosely against each other and leave an apical, inter-cellular space 

 between them, which is dilated upward under the coronula and down- 

 ward over the ovule (infundibuliform). As soon as the ovule is ready 

 for fertilization a sudden change occurs in the upper part of the cap- 

 sule ; the enveloping cells elongate just beneath the coronula by an 

 intercalar growth of the cell membrane. The cuticula (the external 

 cell membrane) does not elongate, but tears transversely, and by the 

 separation of the margins of the tear affords accommodation to the 

 length of the newly formed neck; this is variable in the same species, 

 but generally less marked in Chara than in some species of Nitella. 

 The different parts of the neck diminish upward and in a radial direc- 

 tion ; they do not possess the same thickness that the enveloping 

 tubes below have, so that narrow spaces, dilating upward, form be- 

 tween them, and a larger free inner space develops under the coro- 

 nula. This process goes on at a time when the neighboring Anther- 

 idia rupture (even in Ch. crinita, which is fertilized parthenogeneti- 

 cally [without the aid of spermatozoids], the formation of a neck with 

 inter-spaces takes place). The liberated spermatozoids penetrate the 

 fissures in the neck and reach the interior space, beneath the coro- 

 nula, whence they force their way downward and reach the germinat- 

 ing spot of the ovule. 



In some species of Nitella and Tolypella the upper ends of the 

 capsule cells swell, and the coronula is raised up so that the sperma- 

 tozoids enter from above. 



The spore now becomes full to the top of granules of starch and 

 fat, and its cell wall becomes firm and yellowish (or colorless). The 

 cells of the capsule, which have hitherto been thin and transparent 

 (unless encrusted by lime), become differentiated by an unequal de- 

 velopment of the outer and inner portions. The walls of the investing 

 cells lying against the spore, as well as the upper wall of the cell of 

 the spore pedicle, become thickened, indurated and colored ; a hard 

 shell is thus formed, tightly enclosing the spore and pressing firmly 

 against it. This shell is opaque and like the stony kernel of a fruit ; 

 it is colored differently in different species, light brown, dark or red- 

 dish brown, or black ; it is called the Nucleus. 



