THE ORIGIN OF SEX IN PLANTS 



29 



gametes is brought about. This will be described in the 

 next Lecture. The immediate point is that the relatively 

 small, and in this case non-motile male gamete is conveyed 

 to the relatively larger ovum, both being primordial cells 

 without cell-wall. The two gametes coalesce. At first 

 their nuclei can still be distinguished, but gradually they 

 become fully fused together (Fig. 17). The resulting 





B 



A, Pollen- tube of Orchis with the male gametes (g) within; B, Pollen- tube 

 of Orchis entering the " micropyle " of the ovule, so as to convey the male gametes 

 to the ovum, which is the large cell more darkly shaded. 



zygote gives rise to the embryo, which grows into the new 

 individual. Here again, syngamy consists in the coales- 

 cence of two cells, differing in character, and produced 

 from distinct sources, to form a new cell ; though again 

 the contributory circumstances are different. Such 

 examples illustrate what is the general fact for all the 

 Higher Plants, that the differentiation of sex established 

 in the lower forms is maintained throughout the higher 



