:\rOEPHOLOGY OF REPRODUCTIVE ORGANS 219 



long ovaries of many of the LeguminosEe and Cruoiferae (Jig. 

 418), the ovules are superposed, and, not crowding each other, 

 they are all turned in the same direction ; when, on the contrary, 

 the ovules are numerous, and developed in a small space, they 

 necessarily press against each other, and acquire irregular 

 forms and varying positions, according to the direction of the 

 pressure. In describing these varying positions the same terms 

 are used as those referred to when speaking of the relations of 

 the solitary ovule. These terms are also applied in the same 

 sense to the relations of the seed in the pericarp. 



Section III. 



SEXUAL REPRODUCTIVE OKOANS. 



We have seen that, besides the production of spores, plants 

 bear also reproductive cells which are incapable by themselves 

 of giving rise to a new individual, but which do so after coales- 

 cence in pairs. These cells are hence termed sexual cells, or 

 gametes, and the process of their coalescence is known as con- 

 jugation or fertilisation. The body formed by the coalescence 

 is called a zygote. These sexual cells never arise on the sporo- 

 phyte, but on the other form, the gametophyte. The latter, in 

 some of the Algse and Fungi, bears gonidia or asexual cells 

 as well, the structure and mode of origin of which present 

 no features different from those already described. 



The phase of the plant which we have called the gameto- 

 phyte is seen most prominently in the lower forms, diminishing 

 in size and degree of differentiation as we ascend the scale. 

 The sporophyte can be recognised in only a few of the Algae 

 and Fungi, is of nearly the same dimensions as the gametophyte 

 in the Mosses, and above this group assumes a preponderance 

 and becomes the conspicuous form of the plant, while the 

 gametophyte dwindles almost to the point of suppression. 



In the Algae the gametophyte may be filiform, or take the 

 form of a plate of cells, or assume large dimensions, showing 

 much morphological differentiation. Often in this group the 

 sporophyte cannot be recognised at all. "Where asexual cells 

 occur in such oases, they are gonidia, and are developed upon 

 the gametophyte. Instances of the occurrence of the sporophyte 

 among the Algae are afforded by certain of the cystooarps in the 

 Red Seaweeds, and more certainly in some of the Chlorophyceae 



