CURRENT LITERATURE 



NOTES FOR STUDENTS 



Conditions affecting flower development. — Klebs' divides the process of 

 flower formation by the rosettes of Sempcrvivum Funkii and 5. albidum into 

 3 distinct, successive steps: (i) production of the condition of ripeness to 

 flower (bliihreife Zustand), (2) formation of flower primordia, and (3) develop- 

 ment of flower clusters and elongation of the axis. Light is the dominant 

 factor in determining all 3 of these stages of development. 



In the first and third, light is effective entirely through its photosynthetic 

 action, and its effectiveness rises with its energy value. Higher temperatures 

 counteract light by favoring dissimilation. Accordingly, the effect of tempera- 

 tures can in part be annulled by increased light intensities. It is the balance 

 of assimilation over dissimilation that furthers the development of these 2 

 stages. Klebs finds that at lower temperatures (about 6°C.) both these 

 stages can be attained in darkness, although in the last it gives a far less exten- 

 sive inflorescence. He thinks this is likewise tied up with a balance in favor 

 of available carbon synthate. The low temperature gives low respiration and 

 leads to the accimnulation of soluble sugars by the hydrolysis of insoluble 

 carbohydrates. 



In the second step, formation of flower primordia, light has 2 distinct and 

 antagonistic effects. The one which favors the process is due to the photo- 

 synthetic activity of the light and is a function of the less refrangible rays of 

 the spectrum. The other, which inhibits the process or even annuls the ripe 

 to flower condition, must at present be termed a stimulus effect, and it is a 

 function of the less refrangible blue rays. Diffuse daylight is relatively injuri- 

 ous to primordia development because of the high percentage of blue violet 

 rays it contains. The Osram light and direct sunhght favor this development 

 because of the dominance of the red rays. 



Klebs says it is still an unanswered question whether inflorescence develop- 

 ment in other forms and in plants in general can be divided into these 3 distinct 

 steps with similar light effects in each step. He suggests some facts as evidence 

 that such may be the case. His past work has done much to show that the 

 formative effects of conditions on plants is largely through the nutrient effects 

 of these conditions. Thus the formative effect of light is explained in a large 

 part by its effect on carbon assimilation, but Klebs points out here, as in his 



' Klebs, George, tjber die Bliitenbildung von Sempervivum. Festschrift zum 

 Ernst Stahl. pp. 128-151. Jena. 1918. 



445 



