GYMNOSPEEM^ 175 



secreting ducts in most cases, the secretion being eitlier resin or 

 mucilage. 



The Gametophyte. — As there are two kinds of spore, there 

 are two forms of gametophyte, the male organs occurring on the 

 one developed from the microspore, the female on that proceed- 

 ing from the macrospore. 



The pollen grain generally begins to germmate before it is 

 set free from the microsporangium. It divides into two, one of 

 which is much larger than the other. The smaller is known as 

 the antheridial cell, the larger as the vegeiative one. In some 

 species more than one small cell is produced, the whole series of 

 them being then looked upon as a rudimentary prothallium, and 

 the last formed being the antheridial cell. After escaping from 

 the sporangium the vegetative cell grows out into a long fila- 

 mentous body, known as the pollen tube ; it is composed only 

 of the intine of the spore, the exine rupturing to give it exit. 



The antheridial cell divides into two, a stalk cell and a 

 generative cell. The generative cell and the nucleus of the 

 vegetative cell both make their way down the pollen tube ; the 

 vegetative nucleus breaks up and disappears ; the generative 

 cell divides into two, which represent the mother cells of anthero- 

 zoids of the Pteridophyta. The antherozoid is, however, not 

 differentiated. In some forms there is a still further division of 

 the generative cells at the apex of the pollen tube. The ultimate 

 cells, whether the divisions be one or many, are naked cells and 

 constitute the male gametes. They are e\'entually extruded 

 from the pollen tube. 



The prothallium which is produced from the macrospore is 

 sometimes called the endosperm. It is never exposed as in the 

 Pteridophyta. The nucleus of the macrospore divides repeatedly 

 till a large number of nuclei are present ; these are arranged in a 

 layer in the protoplasm lining the spore ; then between them 

 ceU-walls are formed, and a peripheral cellular layer is thus 

 constituted. The cells of this layer by ordinary cell-division 

 IDroduce a tissue which fills the spore. This is the prothallium. 

 Archegonia are developed at its apical end, having almost the 

 same structure as in the Pteridophyta. They arise from 

 superficial cells, and have a neck and a venter, in which lie the 

 neek-canal-cells, ventral-canal-ceUs, and oosphere respectively. 



Fertilisation is brought about by the microspore germinating 

 upon the apex of the macrosporangium. The pollen tube pene- 

 trates the latter by the micropyle and bores its way into the 

 tissue of the nucellus during its development, as described above. 



