CELL-FORMATION. 



37 



plant— passes and blends with the protoplasm that has not 

 moved from the cells of the other— female plant ; the two 

 originally independent masses of protoplasm combine to 

 form one cell, the zygospore. In other examples the zygo- 

 spore is formed at the point of contact of the two cells, 

 thus indicating less differentiation between the presumably 

 male and female elements. Conjugation only takes place 

 in certain groups of algae and fungi. 



Eejuvenescence. — In this 

 method the entire mass of pro- 

 toplasm of a mother-cell con- 

 tracts as a primordial daughter- 

 cell, which eventually secretes 

 a cell-wall. The zoospores of 

 many of the simpler forms of 

 algse are formed in this way, 

 as are also the oospheres of 

 Cryptogams. 



From the above examples 

 it will be seen that the forma- 

 tion of new cells does not necessarily imply the production 

 of a greater number of cells than existed previously. This 

 is the case in vegetative and reproductive cell-formation by 

 division, also in free-cell formation. In rejuvenescence the 

 number of cells remains unaltered, whereas in conjugation 

 the actual number of cells is diminished. 



Substances contained in Cells. — Various specialized struc- 

 tures are met with in cells, amongst the most important 

 being chlorophyll and starch. 



In some of the simpler forms of algae the green colour- 

 ing matter or chlorophyll is equally diffused throughout the 

 protoplasm, in all other plants it exists in the form of 



s, Zygospore of Mucor, 

 minute fungus ; m, the mycelium 

 (mag.). (From Prantl.) 



