124 pringsheim's researches on chlorophyll. 



and only after prolonged exposure, and when the jilant has 

 become very deep green. This very significant fact may 

 be explained by the relation of the colouring matter to 

 respiration. The formation of hypochlorin in the plant 

 begins with the commencement of illumination. How, 

 then, is evidence of this effect of light not apparent in the 

 first twenty hours ? Because apparently the hypochlorin is 

 consumed in light until there is a sufficient accumulation 

 of colouring matter for its protection, and it is also possible 

 that the hypochlorin first formed ma,y be converted into 

 colouring matter and may thus be the mother substance of 

 the chlorophyll colouring matter, an hypothesis which, as will 

 presently be pointed out, may explain the development of 

 green colour in the dark within the tissues of gymnospermous 

 embryos. 



The relation of hypochlorin-formation to assimilation and 

 respiration may be further elucidated by placing the seedlings 

 grown in the dark not in bright full daylight, but in 

 conditions of half darkness (a darkened room). Here 

 they become quite green, but do not live long, and dis- 

 integrate almost as rapidly as those growing in complete 

 darkness. Such facts have led to the supposition which has 

 been already refuted in this paper, that a plant becomes 

 green in light of a lower intensity than is requisite for 

 assimilation. The explanation really is that, in the relations 

 of assimilation to respiration, this low intensity is unfavour- 

 able for assimilation, and the products of this process are, 

 without any permanent gain to the plant, again used up. If 

 seedlings grown in darkened rooms are brought into bright 

 light, which is favourable to development of green colour but 

 not to evolution of free oxygen, then no hypochlorin is to be 

 found in them. Such plants grown in half-dark conditions 

 whether they have been in half darkness throughout or were, 

 at first in complete darkness) show no trace of hypochlorin, 

 even if the plant is as well formed and as deeply green as a 

 seedling which has for some days grown in full daylight 

 and contains abundance of hypochlorin. It depends on the 

 regulation of the brightness whether or no after a time, say 

 eight to fourteen days, hypochlorin is found in plants grown 

 under half-dark conditions ; for as soon as assimilation is 

 greater than respiration then hypochlorin accumulates and 

 increases in amount with the increasing brightness. Beau- 

 tiful green seedlings destitute of hypochlorin may be grown 

 under a glass shade covered with grey paper in the half-dark 

 illumination on the side farthest from the light of a deep 

 room. Its absence from these is a proof that it is used up 



