534 



LECTURE XXXI. 



which are already beginning to form flowers, in the dark : the production, however, 

 is always more restricted, and the development of normal flowers particularly is in- 

 significant, or conspicuous abnormalities in the growth of the flowers appear, simply 

 because the flower-forming substance has not been previously accumulated in suf- 

 ficient quantity. 



These experiments as to the dependence of the formation of flowers on the 

 preceding or simultaneous activity of the foliage-leaves in the light, now explain 

 to us also one of the most universal relations of growth in plants. The flowers 

 appear either singly or several together in the axils of foliage-leaves, evidently because 

 the formative substance produced in the latter can thus be most easily transferred to 

 them. In very many other Phanerogams there are formed single or many flowers 

 (Inflorescences) on long shafts, so that the completely developed flowers are far distant 

 from the assimilating leaves : this is the case with almost all Grasses, and many Lilia- 

 cese {Allium, Aloe, Draccrna, &c.). But it must not be overlooked that in such cases 

 the flower- buds are already fully developed in all essential points while the eventually 

 very long floral support or shaft is still extremely short, and the entire inflorescence is 

 thus situated either in the axil of a foliage-leaf or in the midst of a rosette of 

 numerous leaves, so that in such cases also the formative substances are conveyed 

 by the shortest route to the young flowers. When then the stalks of the flowers 

 or inflorescences become elongated, and the flowers removed further away from the 

 leaves which supply them with nutriment, it is a matter simply of their unfolding, and 

 this depends essentially upon the necessary supply of water. We may probably 

 go a step further, and assert that the proper reproductive organs in the narrowest 

 sense of the word (the spores, male fertilising cells, and oospheres) take up their 

 formative substance from the assimilating organs, and since only shoots can be 

 assimilating organs at all, an explanation is oflfered of the fact that all true organs 

 of reproduction are produced exclusively by shoots, and are usually formed on leaves 

 or in the axils of leaves, or at any rate in some close connection with them. It 

 may be objected that in the case of plants which contain no chlorophyll, the repro- 

 ductive organs are also connected with the shoots. We can however reply that such 

 plants are phylogenetically derived from plants which contain chlorophyll, and that 

 it is also advantageous for the reproductive organs in general if they arise on the 

 shoots protruding above the substratum. 



These considerations may at first sight appear scarcely to harmonise with the 

 fact that bulbs of Hyacinths, Tulips, &c.,when germinating in profound darkness,never- 

 theless produce magnificent normal flowers, while the leaves at the same time become 

 etiolated, though not strongly. But this favourable result of growth in the dark 

 depends essentially on the fact that in the preceding period of vegetation the foliage- 

 leaves of the bulbous plant were able to assimilate in intense light, and that flower- 

 forming substance was thus already collected in the interior of the bulb, and then, 

 during the apparently dormant period in summer and winter, nourished the flower- 

 buds deep in the interior of the bulb, so that when such a plant is eventually allowed 

 to put forth its shoots in the dark, it is only a matter of the last stages of develop- 

 ment, which here also are accomplished chiefly by the addition of water. This 

 opportunity may be taken of mentioning the fact that many plants provided with 

 bulbs, tubers, or large rhizomes, and especially phanerogamous root-parasites and 



