264 CALIFORNIA ACADEMY OF SCIENCES. [Pkoc. 3D Ser. 



limiting membrane of the cytoplasm) are attached to the 

 spindle wall that the latter begins to form conical projec- 

 tions such as are seen in figs. 7 and 8. Many very con- 

 spicuous fibres seem to be in no way connected with the 

 formation of cones; around these fibres, however, other 

 fibres frequently group themselves to form fibre cones; but 

 this is not followed by the development of conical projec- 

 tions of the spindle wall. 



The width of the genetic layer at this time varies from 

 that shown in fig. 7 to a width not exceeding that in the 

 early stage, shown in fig. 3. 



The subsequent development of the cones is shown in 

 figs. 8 to 10 ; the larger ones often extend completely to the 

 limiting membrane of the cytoplasm, and the smaller ones 

 are usually connected with it by a conspicuous fibre. 



During this period, the exterior fibres diminish in number, 

 lose their power to stain violet, and begin to stain slightly 

 orange. They are apparently retransformed into cytoplas- 

 mic reticulum. They have usually ceased to be recognizable 

 (or at least the majority have) at the beginning of the 

 disappearance of the nuclear wall. 



During the development of the cones the genetic fibres 

 contained in them undergo a certain amount of rearrange- 

 ment, tending to make them converge more or less toward 

 the apex of the cone. At the same time, they lengthen to 

 keep pace with the elongation of the cone, and the gran- 

 ular enlargement at the point of their insertion on the 

 spindle wall gradually disappears as though its substance 

 were being drawn into the fibre to provide material for its 

 elongation. 



The pollen-mother-cells of Agave are very favorable 

 material for the study of the disintegration and disappear- 

 ance of the nuclear wall, and the penetration of the genetic 

 fibres into the nuclear cavity. The nuclear wall first becomes 

 granular, and just before it begins to disappear consists of 

 numerous small granules between which a delicate mem- 

 brane is visible. Thereupon the membrane presents the 

 appearance of being slowly dissolved, growing thinner and 



