232 Influence of Environment on Plants 



One extreme case, that of exceptionally early flowering, has been 

 observed in nature and more often in cultivation. A number of plants 

 under certain conditions are able to flower soon after germination 1 . 

 This shortening of the period of development is exhibited in the 

 most striking form in trees, as in the oak 2 , flowering seedlings of 

 which have been observed from one to three years old, whereas 

 normally the tree does not flower until it is sixty or eighty years old. 



Another extreme case is represented by prolonged vegetative 

 growth leading to the complete suppression of flower-production. 

 This result may be obtained with several plants, such as Glechoma, 

 the sugar beet, Digitalis, and others, if they are kept during the 

 winter in a warm, damp atmosphere, and in rich soil ; in the following 

 spring or summer they fail to flower 3 . Theoretically, however, experi- 

 ments are of greater importance in which the production of flowers is 

 inhibited by very favourable conditions of nutrition 4 occurring at the 

 normal flowering period. Even in the case of plants of Sempervivum 

 several years old, which, as is shown by control experiments on 

 precisely similar plants, are on the point of flowering, flowering is 

 rendered impossible if they are forced to very vigorous growth by an 

 abundant supply of water and salts in the spring. Flowering, how- 

 ever, occurs, if such plants are cultivated in relatively dry sandy soil 

 and in the presence of strong light. Careful researches into the 

 conditions of growth have led, in the case of Sempervivum, to the 

 following results: (1) With a strong light and vigorous carbon- 

 assimilation a considerably increased supply of water and nutritive 

 salts produces active vegetative growth. (2) With a vigorous carbon- 

 assimilation in strong light, and a decrease in the supply of water and 

 salts active flower-production is induced. (3) If an average supply 

 of water and salts is given both processes are possible ; the intensity 

 of carbon-assimilation determines which of the two is manifested. 

 A diminution in the production of organic substances, particularly of 

 carbohydrates, induces vegetative growth. This can be effected by 

 culture in feeble light or in light deprived of the yellow-red rays: 

 on the other hand, flower-production follows an increase in light- 

 intensity. These results are essentially in agreement with well- 

 known observations on cultivated plants, according to which, the 

 application of much moisture, after a plentiful supply of manure 

 composed of inorganic salts, hinders the flower-production of many 

 vegetables, while a decrease in the supply of water and salts favours 

 flowering. 



1 Cf. numerous records of this kind by Diels, Jutjendformen itnd Blilten, Berlin, 1906. 



2 Mobiua, Beitrage zur Lehre von der Fortpjlanzujic/, Jena, 1897, p. 89. 

 '' Klebs, Willkiirliche Aenderungen, etc. Jena, 1903, p. 130. 



4 Klebs, Ueber Idinstliche Metamorphoses, Stuttgart, 190G, p. 115 (Abh. Nattirf. Ges. 

 Halle, xxv.). 



