HEREDITY AND VARIATION 



Syngamy is the fusion of gametes to produce i tli- 



standing the fact that in many Algae the garnet of the natan 



primordial cells with a considerable amount of cytoplasm, and in 

 higher types, such as Mosses, Ferns and Seed Plants, the cytoplasm 

 of the male gamete is reduced to negligible proportions, fertilisation is 



Fig. 433. 



Camera lucida drawings of chromosomes in the prophase of meiosis. A, Ltltum 

 pardalinum ; B, Fritillana lanceolata. Note the correspondence between the sue 

 and sequence of the particles of the pairing chromosomes. In 13 the four strands 

 (chromatids) are clearly seen. There is one chiasma in each case. (From Crane and 

 Lawrence after Belling.) 



essentially a process of nuclear fusion. The first division of the zvl 

 is an ordinary mitosis (apart from cases like that of Spirogyra, where 

 the zygote itself undergoes meiosis on germination), with equal 

 distribution of chromosome-halves (chromatids) ; and all subsequent 

 vegetative divisions follow the same course. As botli the nude and the 

 female gametes are haploid, syngamy restores the full number of 

 chromosomes. The diploid sporophyte i- thus initiated, and the 

 normal nuclear cycle, diploid sporophyte- haploid gametophyte 

 diploid sporophyte, may be repeated indefinitely. 



Chromosome Complkmini (Karyotype). 



It has already been noted that the chromosome number i< constant 

 for all the somatic divisions of any normal plant. Thus the Garden 



