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. (Klebs, "Willkurliche Aenderungen", etc. Jena, 1903, page 130.) Theoretically, however, experiments are of greater importance in which the production of flowers is inhibited by very favourable conditions of nutrition (Klebs, "Ueber kunstliche Metamorphosen", Stuttgart, 1906, page 115) ("Abh. Naturf. Ges. Halle", XXV.) 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, however, 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 cases 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. ii. INFLUENCE OF THE ENVIRONMENT ON THE FORM OF SINGLE ORGANS. (A considerable number of observations bearing on this question are given by Goebel in his "Experimentelle Morphologie der Pflanzen", Leipzig, 1908. It is not possible to deal here with the alteration in anatomical structure; cf. Kuster, "Pathologische Pflanzenanatomie", Jena, 1903.)