Nos. 451-452-] STUDIES ON THE PLANT CELL. 575 



Formation) and in spite of Strasburger's conclusions that it is 

 derived entirely from the plasma membrane we are justified in 

 asking for a fuller description of its development. There is the 

 possibility of a different origin wherein the nucleus may play an 

 important part which, in the light of Timberlake's studies on 

 Hydrodictyon, suggests that Strasburger may not have discov- 

 ered the earliest beginning of the blepharoplast in CEdogonium. 

 And the same doubts apply to Cladophora and Vaucheria. 



There is thus considerable divergence in the views of the 

 origin and nature of the blepharoplast in zoospores, Strasburger 

 believing that they are developed as a specialized region of the 

 plasma membrane with no relation to centrosomes, and Timber- 

 lake holding that the structure in Hydrodictyon is not a part of 

 the plasma membrane but comes from the interior of the proto- 

 plasm. The problem is also involved with conditions in the 

 sperm, where there is likewise a difference of opinion as to the 

 homologies of the blepharoplast but an undoubted origin at 

 least in the pteridophytes and gymnos perms from- the interior 

 of the cell. We should naturally expect the blepharoplasts of 

 zoospores and sperms to be homologous and consequently the 

 problem is of great theoretical interest and will be taken up 

 again in our discussion of the sperm. Its solution demands a 

 most thorough study of the development of some of the larger 

 zoospores as in CEdogonium and certain species of the Confer- 

 valesand Volvocales. 



The pigment spot is almost universally present in zoospores 

 and is also characteristic of the cells of many motile organisms 

 as in the Volvocales and Flagellates while occasionally found in 

 other groups. The structure has been called an eye spot from 

 its fancied resemblance to the simple eyes of certain Crustacea 

 (Cyclops, etc.) but this term is unsatisfactory since it is not 

 established that the pigment spot is primarily a receptive organ 

 for light or warmth ; but even should it prove to be thus sensi- 

 tive (which ,is very probable) thereby orienting the cell with 

 respect to the direction of incoming rays, that is not a function 

 comparable to sight. 



The coloring matter of the pigment spot is held as a single 

 globule or as a collection of numerous small granules in meshes 



