324 THE BIOLOGY OF FLOWERING PLANTS 



have assigned to it lies rather in the possibility it gives of 

 producing fresh types. It is not easy to see why such 

 a property should survive. We should look in some 

 other direction for an explanation of its origin and power 

 of persistence in primitive forms. 



{d) An interesting suggestion has recently been made 

 by Jones (191 8). He points to the resemblance between the 

 sexual fusion of egg and sperm, and a parasitic attack by 

 the latter on the former. It is quite possible that sexual 

 fusion originated in a mutual parasitic attack of feebly 

 assimilating, semi-starved, primitive organisms. If the 

 habit of such parasitic fusions were once deeply stamped on 

 the organism it might have given rise to the whole structure 

 of sexual reproduction, which would in the course of 

 evolution have thus changed entirely its significance for 

 the organism. 



§ 3. Seed Formation 



Taking once more the fern as a type of a land plant, 

 we may resume the foregoing discussion by saying that, in 

 its spores, it has a means of reproduction capable of giving 

 rise to great numbers of new individuals, of scattering the 

 offspring widely, and of resting through periods of adverse 

 conditions ; through its gametes it secures the advantages 

 of crossing. The definite alternation of the two in one 

 life cycle ensures the regular recurrence of the two kinds 

 of benefit. 



The simple condition of the fern is lost in higher plants. 

 First the gametophyte was reduced until it became confined 

 to the spore, and a marked differentiation of the spores 

 took place. Then the megaspore remained attached to the 

 parent plant, embedded in the sporogenous tissue. This 

 was an important change, for at this point the megaspore 

 lost the two chief characters and functions of the spore — the 

 possibility of dispersal and the power of drought resistance. 

 This is the condition in the flowering plants, gynmosperms 

 as well as angiosperms. The details are different in these 

 two great groups but they resemble each other in this, that 



