448 



PART III. — THE CLASSIFICATION OF PLANTS. 



and a female, developed respectively from the microspore and the 

 macrospore. 



The Male Prothallium is, in all cases, filamentous and relatively 

 small, consisting of but few cells. The first indication of its 

 development is the division of the nucleus of the microspore, 

 which may take place even before the microspore escapes from 

 the raicrosporangium, and this is followed by cell- formation. In 

 the Angiosperms (Fig. 288) the cell-formation is simple, consisting 

 in the aggregation of protoplasm round one of the two nuclei, witli- 



^? 



^? 



Fig. 289.— Development of male prothallium from the pollen-grain of the Yew : A early- 

 stage. B Later stage: «t stalk-cell; au antheritlial cell ; n nucleus of the large vegetative 

 cell which has grown out into the pollen-tube. In B the generative cell is travelling down 

 the pollen-tube as a preliminary to fertilisation. ( x 350 : after Belajeff.) 



out any formation of cell-wall, so that a small primordial cell, 

 the generative cell, is formed, floating freely in the protoplasm 

 of the microspore which, with the other nucleus, constitutes 

 the vegetative cell. In the Gymnosperms the process is rather 

 more complicated. In the simplest case (e.g. the Yew, Fig 

 289) the microspore divides into two cells, separated by a cell- 

 wall ; of these the one, the antheridial cell, undergoes division 

 into two, a stalk-cell (st) and a generative cell (an); whilst the 

 other remains as an undivided vegetative cell. In some cases, 



