208 INFLUENCE OF CORRELATION AND EXTERNAL STIMULI 



ovule which is first fertilized is the one, or whether other factors come into 

 operation. 



Even more striking are the incidents in the development of the seeds of 

 many conifers. In the pine we find three to five eggs in the ovule, each of 

 them capable of fertilization. Let us suppose that three of them are 

 fertilized : three embryos are produced in the first instance, and each of 

 them then splits into four partial embryos each of \vhich might develop to 

 a complete embryo and there would then be twelve embryos in a seed ; but 

 subsequently only a single one is found ; it has gained the upper hand and 

 brought about abortion of the others to the extent that in the ripe seed we 

 can scarcely find even their compressed remains. This splitting of the 

 primary embryo is evidently useless ; yet further more accurate research 

 may perhaps prove that the arrested partial embryos play to a certain 

 extent the part of haustoria, that the nutriment in the endosperm may be 

 passed on by them in a form which can then be quickly used by the 

 privileged embryo. 



The several fruits produced by the flowers in a many-flowered inflo- 

 rescence engage in a struggle of the same kind as that witnessed between 

 the several seeds (or the primordia of embryos) included within the fruit. 

 It is quite common to find that the plastic material is not sufficient to bring 

 about the unfolding of the youngest last-formed flowers at the end of the 

 inflorescence ; whilst usually all the organs are laid down in them, they are 

 arrested because the older flowers have already begun the formation of 

 their fruit and therefore demand all the available plastic material which 

 would otherwise have flowed on to younger flowers. If one removes at 

 an early period the fruits as they are forming in such an inflorescence, the 

 younger flowers which in normal circumstances would have been arrested 

 will be developed ; this may be readily observed in Boragineae, Oenothera 

 biennis, and other plants. This correlation is the less evident the more 

 favourable are the conditions of nutrition of the plant. In the examples we 

 have just mentioned the flowers which usually become arrested may be 

 regarded from the utilitarian standpoint as reserves which may come into 

 action in the case of the failure of the act of fertilization in the older 

 flowers ; but one must carefully distinguish such cases from those where 

 the last flowers are arrested from the outset in the bud, as happens in 

 many grasses. Such arrested flowers, which are found in many different 

 stages of development, are, so far as we as yet see, quite useless structures. 



We find also in the vegetative region examples of the temporary or 

 permanent arrest of development through correlation. In trees and shrubs 

 with a periodic growth the axillary buds on the twigs of any one year 

 only shoot out in the succeeding year. By a timely removal of the leaves 

 the development of these buds into shoots may be brought about in the 

 year of their formation, and this happens in nature in plants whose leaves 



