158 Transactions of the Society. 



produced but one or two seeds during its whole life. There is, 

 however, an enormous destruction of seeds. The great majority 

 are eaten by animals, or fail to secure a suitable site for 

 germiuation ; of those which do germinate again, many are 

 crowded out by their fellows. Darwin observed that out of 357 

 seedlings which came up in a space of 3 ft. by 2 ft., no less than 295 

 were destroyed by slugs and insects. Now the greater the chance 

 against any given seed reaching a suitable locality and attaining 

 maturity, the larger number of seeds must the plant produce in 

 order to maintain its numbers, and, as a general rule, the smaller 

 will the individual seeds be. On the contrary, the greater the 

 chance that each seed enjoys of arriving at maturity, the smaller 

 the number of seeds that is necessary, and in such cases it is an 

 advantage that the seeds should be large. 



Hence parasitic plants generally produce a large number of very 

 small seeds, though there are exceptions, due to other considerations, 

 as, for instance, in the Mistletoe (I believe, indeed, in all the 

 Loranthacere), where the seeds are carried away by birds. 



Aquatic plants and those living in muddy situations often have 

 small seeds. 



For the same reason, perhaps, saprophytes which grow on beds 

 of deep humus often have extremely small seeds. They do not 

 require any large supply of food in themselves, as they have a rich 

 supply close at hand. 



It may also be suggested that in species where the conditions 

 are unfavourable to fertilisation those ovules which do develop may 

 attain a large size. 



Form of the Seed. — The next point to be considered is the form 

 of the seed. The spherical may perhaps be regarded as the normal 

 form, because a given amount of nutriment may thus be protected 

 with the least expenditure of material for the construction of a pro- 

 tecting skin or shell. There are, however, many other points to be 

 considered. 



In some cases the form is determined by the cavity of the 

 fruit which the seed fills. Where the hollow is spherical, and 

 there is a single seed, this is spherical also — as, for instance, in 

 Acer. If there are two seeds, each is hemispherical. When there 

 are more, each is angular, as in the Beech. If the seeds are 

 numerous, as in Delphinium, they are polygonal, by mutual 

 pressure while still soft and immature. 



In the case of marsh and water plants the seeds are sometimes 

 produced at each end. as, for instance, in Juncus (fig. 26), Drosera 

 (fig. 24), Hypericum, Elodea, and especially in Narthecium (fig. 25). 

 This perhaps is useful as preventing them' from sinking too deep 

 into the soft and mossy ground. In others, as, for instance, Elatine, 

 though not produced ai the ends, the seed is elongated, which 

 perhaps serves the same purpose. 



