480 RECORD OF CURRENT RESEARCHES RELATING TO 



epidermal cells of the leaves of terrestrial Phanerogams and Vascular 

 Cryptogams, with the exception of the guard-cells of the stomata. 



M. Stohr has examined the leaves of 102 species of terrestrial 

 Dicotyledons belonging to a number of different natural orders, and in 

 94 of them has found chlorophyll in the ordinary cells of the epidermis. 

 Among gymnosperms it was found only in species with very large 

 leaves, and in Monocotyledons not at all. In most cases it occurs in 

 the epidermis of the under side only of the leaf, but also in that of the 

 leaf-stalk and stem. This epidermal chlorophyll appears in some 

 cases to be functionless, no starch being found enclosed in the grains, 

 but in its place strongly refractive particles not coloured by iodine, 

 probably a product of transformation of the original starch. The 

 cause of the normal absence of chlorophyll from the epidermis of the 

 upper sides of leaves appears to be its destruction by too intense light. 



M. Stohr confirms the ordinary statement that chlorophyll is 

 universally present in the epidermis of the submerged leaves of aquatic 

 plants. This again supports the view advocated by Pringsheim that 

 chlorophyll is destroyed by too intense light. 



Relationship of Hypochlorin to Chlorophyll.*— In the fourth 

 instalment of his researches on chlorophyll, Pringsheim gives further 

 details of the nature of the hypochlorin which he regards as one of its 

 essential constituents, t It can readily be separated from the chloro- 

 phyll grains in the living green cell by the action of hydrochloric 

 acid, appearing as a dark reddish-brown or rust-coloured excre- 

 tion, at first of an oily nature, but subsequently forming ill-defined 

 needle-crystals. The substance has more resemblance to an ethereal 

 than to a fat oil. The hypochlorin can also be separated by other 

 reagents, as picro-nitric acid. It also separates spontaneously from 

 the chlorophyll grains in preparations of green tissues which have been 

 preserved for months in glycerine or calcium chloride. By the aj^pli- 

 cation of moist heat, as by warming in water or distilling with aqueous 

 vapour, another substance also separates analogous to hypochlorin, 

 but differing from it in being uncrystallizable. The chlorophyll-grain 

 from which the hypochlorin has been eliminated, has then the form 

 of a spongy porous skeleton, or with somewhat the structure of a 

 sieve-plate. 



In this paper the author gives additional reasons for the conclu- 

 sion at which he had previously arrived, that the hypochlorin is formed 

 independently in the chlorophyll-grain, and that, in angiosperms, 

 light is absolutely necessary to its production. The colouring matter 

 of the chlorophyll, by its absorptive power on light, protects the hypo- 

 chlorin from oxidation in too intense light. 



Gymnosperms exhibit a peculiarity in regard to the formation of 

 hypochlorin, as they have long been known to do with respect to 

 chlorophyll. Just as they are the only phanerogams whose seedlings 

 can form, in an unexplained manner, chlorophyll in the dark, so they 

 are also the only ones in which hypochlorin is also formed under similar 

 circumstances. 



* ' MB. K. Preuss. Akad. Wiss.' (Berlin), 1879, j). 860, t See ante, p. 117. 



