436 



VEGETABLE PHYSIOLOGY 



the immediate neighbourhood of one another, so that the 

 transport of the antherozoids to other prothallia than 

 their own is not at all difficult. After their liberation they 

 are attracted to the archegonia by some constituent of the 

 mucilaginous matter which is excreted from their necks 

 when they open (fig. 181). In the Mosses this has been 

 ascertained to be cane-sugar, in the Ferns it is malic acid 

 or one of its salts. In the Eliodopliycea and such Asco- 

 mycetes as exhibit sexual reproduction, the passive male 

 gamete, often called a spermatium instead of an anthero- 



FIG. 182. DEVELOPMENT OF THE ABCHEGONIUM OP THE FEKN. (After Kny.) 



zoid, is floated to the female organ or its trichogyne by 

 currents in the water. 



In the Phanerogams, where the female gametophyte is 

 always attached to the parent sporophyte, such a means 

 of fertilisation is of course impossible. For fertilisation to 

 take place it is necessary that the two gametophytes shall 

 be produced in close propinquity to each other. This is 

 effected by the bringing together of the two spores con- 

 cerned in developing them. The microspore or pollen 

 grain is carried by various means to the neighbourhood of 

 the megasporangium ; in the Gymnosperms it falls upon 

 the megasporangium itself ; in the Angiosperms upon the 

 stigma of the pistil in which the megasporangia are hidden. 

 When it germinates the prothallium or gametophyte takes 



