44 



those colors that have the greatest ilkiminating power are those that 

 least favor germination. 



Ad. Brongniart (1832) announced as the results of his experiments 

 that the retarding influence of light depends not only on the illumi- 

 nating power of the colored light, but on the relative quantitj^ of white 

 light that passes through the different colored glasses. In all these 

 experiments the seeds were seA^ral millimeters below the surface of 

 the soil, so that the colored lights did not affect the seeds directl3% but 

 indirectl}' through the soil whose temperature and moisture and 

 evaporation may easily be of predominating importance. 



Ph. A. Pieper (ISS-t), Meyen (1837), ^Zantedeschi (1846), and 

 Belhomme (1854) have all experimented on the growth of seeds 

 under colored glasses; but the sources of error incident to this 

 method of observation prevent us from drawing any conclusion as to 

 the influence of light itself. 



Ville (1865) says that the injurious effect of solar radiation on 

 germination is the result of the heat onh?^ and that the effect of the 

 light is inappreciable. For aquatic plants whose seeds germinate in 

 the Avater, darkness seems decidedl}^ favorable to germination, but it 

 acts only in an indirect manner by preventing the warming of the 

 water and the disengagement of the oxygen that is dissolved in this 

 water. 



Charles Darwin (1877) says that certain species of seeds do not 

 grow well when they are exposed to the light, even the diffuse light of 

 a room. 



Duchartre (1877) considers the action of darkness as a secondary 

 influence, useful but not at all essential and concerning which there 

 has been too much exaggeration. 



Faivre (1879) has shown that the appearance of the primordial 

 latex occurs at a moment when the radicle is only a few milliuieters 

 long and when the cotyledons are still inclosed in the seed envelopes 

 and have not yet received the action of light. He notes that under a 

 yellow light obtained by transmitting sunlight through a solution of 

 bichromate of potash the seeds develop their chlorophyl and their 

 latex more rapidly, and consequently have a shorter period of ger- 

 mination than under a blue light obtained by transmitting sunlight 

 through a solution of the ammoniacal oxide of copper. 



Detmer (1880) has consecrated an extensive Avork to the study of 

 the germination of seeds, and states that concerning the action of 

 light we are still ignorant as to whether it is direct — that is to say. 

 whether it stimulates the storing up of new substances in the vege- 

 table tissue or whether, on the contrar}^, it strengthens the persist- 

 ence within the cells of some special process having a more or less 

 intimate relation to the phenomena of growth and which can only 



