212 INFLUENCE OF CORRELATION AND EXTERNAL STIMULI 



various stages of development in consequence of the conversion of the 

 stalk into a flag-apparatus. In the inflorescence of the cauliflower the 

 flower-stalks are abnormally thickened and fleshy ; and in Celosia the axes 

 of inflorescence are expanded into a broad band upon which many abortive 

 flowers are formed beside normal ones. The list might be extended ; 

 Rhus Cotinus, for example, will suggest itself. There are however no 

 experimental proofs of any of these cases and in the absence of them our 

 conclusions are merely conjectures, although no doubt very probably 

 correct ; and the same must be said regarding the conclusion that in seed- 

 less fruits of pine-apple and cultivated banana the abortion of the seeds is 

 caused by the increased development of the flesh of the fruit. 



The cases last mentioned lead us to a consideration of the relationships 

 which obtain between the flowers or the organs of reproduction in general 

 and the vegetative parts. On the one hand there are many cases which 

 show us that a restriction of vegetative development may be bound up with 

 the formation of the reproductive organs or their products ; as examples of 

 this we have the dying of the prothallus of a fern after the embryo is formed, 

 and the death of annual plants following upon the formation of their flowers 

 and seeds. On the other hand the formation of the reproductive organs 

 may be suppressed in circumstances which provoke a luxuriant development 

 of the vegetative organs, whilst a restriction in the growth of these may 

 bring about the formation of the reproductive organs. In this part of the 

 subject a considerable amount of knowledge has been accumulated l which 

 it is not my intention to bring together here, as it more properly belongs 

 to the physiology of reproduction. Some few examples will serve my 

 purpose. 



The Coniferae in particular furnish us with examples illustrating the 

 favourable influence of restricted growth upon flower-formation, as I have 

 already pointed out. Transplanted spruces, for example, flower much 

 earlier than is normally the case, although the flowers do not usually 

 produce fruit, and I have seen similar phenomena in Thuja occidentalis ; 

 on poor soils transplanted plants are profusely covered with flowers. 

 Similar instances are familiar to every gardener. Annual plants will reach 

 the stage of flowering much later, other conditions being equal, if they are 

 growing in rich soil where a luxuriant vegetative growth is possible, than 

 will be the case if they have but little nutriment available ; nutrition acts as 

 a stimulus, to use a modern expression, which compensates for a longer 

 vegetative development and which naturally also makes possible a richer 

 formation of seeds 2 . 



1 With regard to the lower plants see Klebs, Die Bedingnngen der Fortpflanzung bei einigen 

 Algen und Pilzen. Jena, 1896. 



2 See also p. 142. 



