POST-FLORAL CHANGES 407 



The development of the orchid fruit is interesting in 

 this connection. When the flower opens the ovules are 

 quite immature and rudimentary. After pollination the 

 ovary swells, and then the ovules develop and fertilisation 

 occurs, the process often taking some weeks. The swelling 

 of the ovary may be induced by the pollen of species com- 

 pletely sterile with the particular species, e.g. the pollen of 

 Cypripedium can cause swelling in the ovary of Orchis. 

 Here the beginning, at least, of fruit formation is the conse- 

 quence of pollination, and not of fertilisation. On the 

 other hand, we have the familiar fact that an apple often 

 swells very little on a side, the ovules of which, by some 

 chance, have not been fertilised ; and here the growth of the 

 fruit is closely correlated with that of the seed. In marrows 

 and cucumbers basal regions of the fruit, the ovules in which 

 have not been fertilised, also fail to swell. 



The development of the fruit is therefore a process 

 which cannot be referred to the same causal factors in all 

 cases. Normally it is related to the growth of the seed, 

 but it may also be connected with pollination. In the case 

 of the parthenocarpic fruits there may be an influence of 

 the wound hormones postulated by Haberlandt. 



§ 18. Dispersal 



General Remarks. — We may look at seed dispersal from 

 two somewhat diff"erent points of view. The spread of a 

 species to new territory takes place almost solely when the 

 seed is cast loose from the parent ; dispersal serves to 

 distribute the species, and the further the seed is carried 

 the more effective is the distribution. But the scattering of 

 seed to a distance of a few feet, or even inches, may be yet 

 more important, for it means that the young seedlings will 

 come up a little apart, and so will not be subject to extreme 

 competition with each other ; moreover, it seems likely that 

 seed scattered is much less conspicuous than seed lying in a 

 heap, and will thus escape to a greater extent the search 

 of foraging birds. 



