80 



i. e., short waves, had access to the tubers. Vochting finds that, 

 although the light does delay the growth and diminishes the distance 

 between the tubers, still the supply of water is the important factor. 

 (Wollny, X, p. 230.) 



Sachs (1887), as the result of experiments on flie efiect of ultra- 

 violet radiation upon the formation of buds, states that these rays 

 exert on the green leaves (in addition to the assimilation produced 

 by the yellow and neighboring rays) still another effect that consists 

 in the development of particles that contribute to the formation of 

 blossoms. These bud-forming particles move from the leaves into 

 those parts of the plant where they are to bring about their own 

 development into buds. We therefore now know of three different 

 portions of the solar spectrum having very different physiological 

 influences : The yellow and neighboring rays, which bring about the 

 transformation of carbonic acid or the formation of starch ; the blue 

 and visible violet, that act as stimulants to motion; the ultraviolet 

 rays, that produce in the gi'een leaves the material for the formation 

 of buds. (Wollny, X, p. 230.) 



INFLUENCE OF DRYNESS AND SUNLIGHT ON DEVELOPMENT 

 OF TUBERS. 



In the climate of Germany the flowering of different varieties of 

 potatoes is very much restricted. Only a small number of varieties 

 flower regularly and bear fruit, whereas in Chile the plant flowers 

 abundantly, but the tubers are small; in other words, in the Tem- 

 perate Zone the formation of tubers is favored at the expense of 

 fertilization ; the energy of the one process increases while the other 

 diminishes. 



Knight and Langenthal have found that by detaching the young 

 tubers they increase the blooming, and on the other hand, by cutting 

 off the flowers the}' increase the development of the tubers, thereby 

 largely increasing the harvest. Wollny, in 1886, experimented on 

 four plats, each for many varieties of potatoes. He found that cut- 

 ting off the flowers increased the crop of tubers as to number, 

 size, and weight, but that something depended upon the time of 

 cropping the flowers, which is best done a considerable time before 

 they arrive at maturity. It seems probable that dryness and sun- 

 light stimulate the formation of flowers, but humidity and cloudi- 

 ness, at least up to a certain limit, stimulate the formation of tubers. 

 This harmonizes with some recent results obtained by Sachs, who has 

 shown that the ultraviolet rays stimulate the flowering. (Agr. Sci., 

 Vol. II, p. 273.) 



