394 SCIENCE PROGRESS 



carbon assimilation is decisive. In the paper under special 

 consideration here the environmental factor specially con- 

 sidered is light. By the use of the artificial illumination of an 

 Osram lamp, Klebs was able to bring Sempervivum to flower 

 at any time of year, but a certain light intensity is necessary 

 for development of the inflorescence. A continuous low light- 

 intensity is sufficient for the flower rudiments to form, but 

 without the necessary light-intensity the inflorescence does 

 not develop further. Curiously enough it is only at higher 

 temperatures that intermittent light and darkness can be 

 made to inhibit flower-formation ; at low temperatures (4 to 

 6° C.) darkness does not hinder flower-production. As regards 

 wave-length, red light accelerates the production of repro- 

 ductive shoots, while blue light retards it. 



Among other recent work dealing with the influence of 

 light on growth and development may be mentioned that oi 

 C. Olsen (Tidssk. f. Skov. og Trcehdl. 30, 1-48, 191 8), who 

 finds the nettle (Urtica dioica) grows best in half-shade, while 

 nitrate and water content of the soil are also important factors. 

 It is also possible that light is an important condition in bring- 

 ing about full development of colour in the flowers of edelweiss 

 (Leontopodium alpinum). O. Rosenheim {Biochem. Journ. 

 12, 283-9, I 9 J 8) transplanted some plants of this species, 

 collected in the Alps at an average altitude of 2,000 metres, to 

 a garden in a London suburb. In this latter habitat the 

 colour of the flowers was much less intense, and on analysis it 

 was found that the quantity of chromogenic substance in the 

 flowers was only a quarter of that contained in flowers growing 

 in their native environment. Rosenheim argues that this may 

 be an adaptation of the plant to less intense insolation, the 

 pigment in the flower in its native habitat serving a protective 

 function against too intense sunlight. While it is by no 

 means certain that this is really the function of the pigment, 

 it appears to be premature to speak of adaptation to the less 

 intense insolation in the case of the plants grown in London ; 

 on the other hand, it may well be that light is an important 

 factor in determining the extent of development of the colour. 



The influence of temperature on growth has attracted much 

 attention in recent years. E. Talma (Kon. Akad. Wetensch. 

 Amsterdam, 24, 1840-4, 191 6) has measured the increase 

 in length of radicles of Lepidium sativum grown in different 

 temperatures and taken the values so obtained as measures 

 of the rate of growth. The radicles were about 8 mm. long 

 and the increase in length was that taking place in 3-5 hours. 

 It was found that at o° C. growth still took place, and that 

 the growth-rate increased with increasing temperature up to 

 28 C. Above this temperature the rate of growth fell rapidly 



