ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 617 



the fact that Draper, Sachs, and others find a maximum assimilation in the 

 yellow. He believes the apparent contradiction to arise from the circum- 

 stance that the observations of these experimenters have been made on 

 leaves of considerable thickness, where the grains of chlorophyll lie one 

 behind another. The thicker the absorbing layer of chlorophyll, the more 

 — admitting the relationship between the absorption of light and its assi- 

 milating power — must the maximum of the disengagement of oxygen 

 approach the maximum of energy in the spectrum, moving therefore from 

 the region B-C in the red towards the region D in the yellow. If the 

 incident light were completely absorbed by the leaf, the amount of dis- 

 engagement of oxygen in each spot of the spectrum would be proportional 

 to the luminous energy of that spot. If there is a smaller amount of 

 available carbon dioxide than a grain of chlorophyll can decompose, it is 

 evident that the whole of this carbon dioxide will be decomposed ; and, 

 under these conditions, as large an amount of oxygen will be given off in 

 the yellow or green part of the spectrum as in the red ; and the maximum 

 assimilating power will be displaced towards the regions of less absorption, 

 i. e. toAvards the yellow and green. 



Action of the Ultra-violet Rays in the Formation of Flowers.* — 

 Prof. J. Sachs gives details of the experiments from which he has come to 

 the conclusion that the ultra-violet and invisible rays of the solar spectrum 

 are especially efficacious in the development of flowers. The experiments 

 were all made on Tropseolmn majus. If the rays of the sun are made to 

 pass through a solution of sulphate of quinine, the ultra-violet rays are 

 entirely absorbed or transformed into rays of less refrangibility, and which 

 are visible and of a light blue colour. If a plant is made to grow behind a 

 screen of sulphate of quinine the vegetative organs are normally and 

 luxuriantly developed, but the flowers are almost entirely suppressed. 

 Twenty-six plants thus grown produced only a single feeble flower, while 

 twenty plants grown under similar conditions behind a screen of water of 

 the same thickness produced fifty-six flowers. 



Prof. Sachs believes that extremely small quantities of one or more 

 substances formed in the leaves cause the formative materials which are 

 conveyed to the growing points to take the form of flowers. Acting like 

 ferments, an extremely small quantity of these flower-forming principles 

 may act upon large quantities of plastic substances. It may be assumed 

 then that there are three distinct regions of the solar spectriim, differing in 

 their physiological action — the yellow rays and those near them cause the 

 decomposition of carbon dioxide, and are active in assimilation ; the blue 

 and the visible violet rays are the agents in movements of irritation ; the 

 ultra-violet rays are those which produce in the green leaves the substances 

 out of which the flowers are developed. 



Chlorophyll-function of Leaves.j — Herr A. Nagamatsz has determined 

 by experiment the three following points, viz.: — (1) Leaves of land-plants, 

 when completely submerged, do not assimilate ; (2) after light has passed 

 through one leaf, it has no power of inducing assimilation in a second leaf ; 

 (3) no starch is produced in withered leaves. The experiments were made 

 on a number of different plants. 



Absorption-bands. — Herr F. Stenger % contests Eeinke's conclusion that 

 a maximum of absorption does not always correspond to a visible absorp- 



* Arbeit. Bot. Inst. Wurzburg, iii. (1887) pp. 372-88 (2 figs.). 



t Il.id., pp. 389-407. 



X Bot. Ztg., xlv. (1887) pp. 120-6. Cf. this Journal, 188G, p. 651. 

 1887. 2 S 



