68 THE STEUGGLE TOB EXISTENCE. 



The force of gravity also acts directly in the dissemination of 

 seed on inclined ground, the heaviest and roundest seeds obvious- 

 ly rolling away farthest. Very steep slopes can be sufficiently 

 abundantly sown, by a species producing such seed, only under 

 specially favourable circumstances, as where the ground is covered 

 with a close growth of undershrubs, and so on. 



(d) Season of fall of seed. — In forests where fires are an annual 

 occurrence, seeds shed at any time before that plague has passed 

 through, are bound to be almost wholly destroyed, only a few 

 escaping which fall on bare ground clear of combustible substances, 

 or find their way into cracks or under stones, &c., or which belong 

 to species, the seeds of which, like those of teak, Terminalia helerica 

 and Chehula, &c., can stand a high temperature without being kill- 

 ed. Species Hke sal, eng, tun, Tetranthera monopetala, &c., the 

 greater proportion of the seeds of which falls at the beginning of 

 the rains, when the season for fires is over and all nature is green 

 and damp, possess a very marked advantage over their associates. 

 The gregariousness of Quercus dilatata and semeearpifolia is to a 

 great extent to be explained by the fact that their acorns ripen and 

 fall during the rainy season. 



And, in a general manner, it may he said that the longer the in- 

 terval between the fall of the seed and the ensuing rainy season is, 

 the greater will be the number of risks to which it will be exposed 

 from fires, insects, squirrels, rats, and other animals, excessive heat, 

 &c., and hence the less chance will there be of finding a large pro- 

 portion of it fit to germinate when that season arrives. 



(e) Relative vitality or germinative power of the seed. — This con- 

 dition has a most important influence on the reproduction of a 

 species. Although many species produce immense quantities of 

 seed every year or very nearly every year, yet, save in years of ex- 

 ceptional abundance, the majority of the seeds are either quite 

 barren or lose their vitaKty before they can germinate or give rise 

 to seedKngs which die before they are one or two years old. 



But even when the seeds are perfectly sound, their ^-itality will 

 vary very much according to the species. Thus teak, although its 

 seed is shed when jungle fires are about to commence and has to 

 lie for several months on the ground exposed to various causes of 

 destruction before the first fall of rain, is still able to reproduce it- 

 self freely, thanks to the extraordinary -^-itality of its seed, which 

 even a certain degree of scorching will not kill, and which remains 

 perfectly sound after several years of exposure to alternate damp 

 and drought in the forest. Ou the other hand, the seed of the Ter- 



