1910.] Forms of Plants as a Result of Environment. 553 



highly favourable conditions of nutrition, it is impossible for the plants to 

 flower in the summer, in spite of the advanced preparations for it, Th^ 

 rosettes will be transformed into purely vegetative ones, which grow very 

 luxuriantly and produce daughter-rosettes later on. 



Here we have essentially the same behaviour as with the fungi and algse, 

 which, as we know, under corresponding conditions continue to grow without, 

 reproduction. The experiment can be modified without altering the result,, 

 when we cultivate a rosette, ripe to flower, from January to March in a hot- 

 house. An average temperature of 20°, taken in connection with the 

 relatively high degree of moisture, also prevents flowering and produces- 

 vegetative growth, less, however, than in the warm soil-bed. In April we 

 are no longer able to alter the development by such experiments, because the 

 internal preparations for flowering are far more advancd. We must apply 

 other methods, consisting of cUminishing the production of organic substances, 

 by light. 



The simplest way is the culture in complete darkness at a constant 

 temperature of 26°. By putting rosettes, ripe to flower, into the thermostat 

 every day from the beginning of April we can determine the moment at 

 which the transformation takes place. Experiments, continued during 

 several years, show that about the middle of April (when no rudiments of 

 flowers exist), the rosettes, originally ripe to flower, become vegetative again. 



But this result differs from that already explained in an important point. 

 The rosettes lengthen some centimetres, and, when brought later on into the 

 light, form a terminal rosette in place of the flowers. A stay of two or 

 three weeks in darkness during the month of April suffices to cause this 

 alteration of the plant. It is curious that, in spite of the later good culture 

 during the summer, the altered plant does not flower during the same year. 



The same result, but with a stronger growth of the axis, is attained by 

 bringing the rosettes, ripe to flower, into a small house of blue glass which 

 according to spectroscopical examination transmits only the more refrangible 

 rays, from green to violet. In comparison with normal white light, the 

 production of organic substances, such as starch and sugar, is diminished 

 under the influence of blue light, as mierochemical and macrochemical tests, 

 distinctly show. In consequence of this diminished assimilation of carbon 

 dioxide the rosettes become purely vegetative, but they grow better than in 

 darkness, and by the end of the summer can attain a length of as much as 

 20 to 30 centimetres. 



During the same time, and under otherwise equal conditions, the plants 

 were cultivated in houses of red glass, which admitted only the red rays. 

 In this light the carbon assimilation is greater than in the blue light but less 



