TIIK DISPERSIOX OF SEEDS AND SPOnKS. 53 



fertilisation. Plants in which vegetative repi'oduction 

 alone occurs, and those in which adjacent cells 

 conjugate, might be designated (1) Isosperms, since 

 only one set of bodies requires dissemination to 

 secure the perpetuation of the species. Those, again, 

 requiring separate distributions of sperm and germ- 

 cells might be termed (2) Heterosperms. Even a 

 double distributiou would be insufficient for those 

 parasitic fungi which, like Puccinia, spend part of 

 their existence on one host and another term on a 

 different plant. Some of these produce live or six 

 different kinds of spores — secidiospores, uredospores, 

 telutospores, sporidia, sijermantia, etc. In such cases 

 probably three or more distinct and separate dis- 

 tributions or sowings of reproductive bodies may be 

 necessary in order to complete the life-history of 

 the species. These we may provisionally term (3) 

 Pohjspei'ms. 



The nature of the bodies dispersed, whether they 

 be fertilising or fertilised cells, vegetative or resting 

 spores, does not so much concern us at present as 

 the iDrovisions for securing dispersion. Before 

 considering the various agencies by which the 

 distribution of plant-germs is effected, we have to 

 note two general characteristics of all vegetable 

 reproductive bodies, viz., (1) Size and (2) Number. 



(1) The first evidence of adaptation for wide 

 distribution is size. The chances which a minute 

 body has of being carried to a distance are infinitely 

 greater than those of a large body. Hence, in 

 genera], the small size of spores and seeds. So 

 minute are the reproductive bodies of many 

 organisms that they have hitherto defied the powers 

 of the microscope. The contents of the ripe seed- 

 capsule of the orchid resemble snuff. Similar spore- 

 like seeds occur in many epiphytes and parasites 

 such as Rafflesia. The minute size of pollen-grains 

 facilitates their dispersion. The superior adaptation 

 of the pollen-grain in relation to distribution is 

 seen when we compare its size with the seed or 



