than the free air. The ivsults of analysis at the end of the oxperi- 

 nients showed tliat nncUn- the transparent o^hiss tlie weight of the roots 

 was the same as in the free air, but the weight of the leaf was much 

 more, the weight yf the sugar much less, and the weight of the nitrous 

 salts much greater. Under the black glass the weight of the roots 

 was 4 per cent of that in the free air, and the weight of the leaves 

 was about 25 per cent, the weight of sugar 2 per cent, and the weight 

 of the salts 8 per cent, thus demonstrating an almost complete stop- 

 page of the vital processes. 



Evidently the action of these artificial coverings on the experi- 

 mental plants is perfectly analogous to the action of cloud and fog in 

 nature. 



It is commonly said that on the seacoast the action of the salt brine 

 blown by the wind up over the land is to stunt or prevent vegetable 

 growth, but the same effect must be produced by the absence of sun- 

 light in those regions where fog and cloud prevail. 



INFLUENCE OF SHADE ON DEVELOPMENT. 



According to Marchand (1875, p. 130), the influence of a dimi- 

 nution of sunlight on the development of the plant is apparent in the 

 relative growth of plants on sunny and cloudy days or in sunny and 

 shady places, but the matter was brought to exact measurement by 

 Hellriegel. His experiments on barley gave him these results: 



Weifjht of hancst of hurley. 



Plants raised- 



In the open air 



In a greenhouse in direct sunshine . . 

 In a greenhouse in diffuse light only 



"We see here that plants living in the greenhouse, receiving sun- 

 light that has traversed the glass, have experienced a considerable 

 diminution in their development as compared with those in the free 

 air which experienced the full chemical force of the sunshine. The 

 plants living under glass and in the diffuse light developed only a 

 small quantity of stalk and did not perfect the seed at all. 



INFLUENCE OF LONG AND SHORT WAVES OF LIGHT. 



Vochting (1887) investigated the formation of tubers as influenced 

 especially by sunlight. Sachs had maintained that the germination 

 was entirely prevented, or at least went on very slowly, if sunlight, 



