77 



mTLUENCE OF ABSORBENT MEDIA ON CHLOROPHYLL. 



The action of sunlight on the c-hk)rc)phyll within tlie cell is not 

 materially modified if the light passes first through layers of cells 

 that do not contain chlorophyll, such as those of the red colored cab- 

 bage leaf, since in those cells, as in yellow cells and others, t\ui radia- 

 tioii that is absorbed is not to any extent that special radiation which 

 the chlorophyll absorbs. The absorption of light by the yellow 

 cells of the yellow leaves of an alder bush was examined by T. W. 

 Engelmann (Agr. Sci., Vol. II, p. 139), who found that tJicse ab- 

 sorbed most from the middle of the spectrum and least at either end, 

 whereas the chlorophyll absorption is complementary to this. He 

 also found that the green leaves of the alder bush, when exposed to 

 the light side by side with the yellow leaves, set free far more oxygen 

 than these, so that it seems probable that if the yellow cells con- 

 tain only pure xanthopyll there assimilating power would be zero, 



INFLUENCE ON THE SUPPLY OF SAP. 



The action of sunshine in producing or altering the colors of fruits, 

 esj^ecially the black Hamburg grape, has been experimentally studied 

 by Laurent. (Agr. Sci., Vol. IV, p. 147.) Bunches of innnature 

 grapes quite shielded from the sunlight ripened, colored, and flavored 

 as usual, but bunches whose food supply had been cut ofl' by ringing 

 the base of the stock supporting the bunch, and then also kept in the 

 dark, remained green, small, and sour. Bunches that had been sub- 

 jected to the ringing process, but which wer^ exposed to the sunlight, 

 produced berries of normal size, some reddish and others green and 

 of an acid flavor. He concludes that the coloring matter of grapes 

 may be formed in the absence of sunshine, provided a sufficient sup- 

 ply of nourishment be at hand, but if this supply be arrested then the 

 color remains imperfect. 



CLIMATE AND THE LOCATION OF CHLOROPHYLL CELLS. 



Guntz (1886) has studied the anatomical structure of the leaven of 

 cereals and grasses in their relations to locality and climate. This 

 connection is infinitely complex. Among other items brought out by 

 him we note that the green assimilating organism consists of many 

 cells of various shapes and in most cases fills the spaces between the 

 nerves of the leaves; in tropical grasses the green cells occur most 

 in the inclosing sheath, but in the grasses of the steppes it lies on 

 either side of the grooves or ridges. The intercellular gaps, acconling 

 as they are larger or smaller, indicate a moist or a dry soil and, 

 equally so, a moist or dry atmosphere. The bast in the leaves of the 

 gi-asses serves primarily to strengthen the whole structure, but the 

 bast increases with the dryness of the locality, and its proportional 

 distribution is an appropriate, indirect indication of the climate. 



