353 



PHOTOLYSIS IN LEMNA TRISULCA. 

 By Spencer Le M. Moore, F.L.S. 



(Plate 285.) 



In illustration of the variations in position undergone by the 

 chlorophyll of Lemna trimlca in consequence of the alternation of 

 day and night (photolysis), certain figures have been published by 

 8tahl»* which I am unable to acquiesce in as representing the 

 facts according to my impression of them. Although perhaps 

 a point of minor interest, it may be well to call attention to this, 

 inasmuch as the error — as it seems to be, crops up in the recently- 

 published text-books on Vegetable Physiology. Thus Sachs f 

 reproduces Stahl's figures, with implicit acceptance of the Jena 

 Professor's conclusions, and Pfeffer J and Vines § do the same. 



Borodin |J was the first to study photolysis in our type. He found 

 that in diffused light the grains range themselves upon the two 

 walls of each cell lying parallel to the frond's surface, whereas by sun- 

 light they are first driven on to the side walls, afterwards collecting 

 in little heaps in the angles of the cells. It will be remembered 

 that the first of these positions is known as " Epistrophe " and the 

 second as " Apostrophe " (Frank), while for the massing Schimper 

 has coined the word " Systrophe." StahlH took up the subject in 

 more detail than did his predecessor, since he brought the effects 

 of darkness within the scope of his research. He maintains that 

 a difference in the distribution of their chlorophyll is shown by the 

 cells in the thin marginal portion of the frond, as compared with 

 those of the thicker parts. It may be remarked that this marginal 

 portion is mainly made up of a single layer of large chlorophyll- 

 containing cells, but such cells lie first in two, further in in several 

 layers, in the thicker part, which is traversed to a certain distance 

 by the delicate vascular bundle, and also contains wide intercellular 

 spaces ; over the whole frond extends the wavy-bordered epidermis 

 from which chlorophyll is absent. Now in rather poor diffused light 

 the grains in both portions of the frond take up their position upon 

 superficial walls, to shift therefrom in stronger light on to the per- 

 pendicular walls. It is, however, not in accordance with my 

 experience that apostrophe should be described as the result of the 

 action of intense light, hi intense light, i.e., direct sunlight, the 

 grains are at first apostrophised, it is true, but they are soon after- 

 wards systrophised. Moreover, as was shown in my first memoir * 

 on this subject, apostrophe is induced by grades of illumination con- 

 siderably lower than sunlight. Indeed, on a bright day, it is a 

 somewhat difficult matter to select, in a well-light I laboratory, a 

 place where illumination is of poor enough quality to fully epi- 

 strophise the chlorophyll. Finally, apostrophe can be brought 

 about in low light. It may be incidentally remarked that we have 



Bot. Zeitung, lsso. t Vorlesungen, No. xxxv. J PI nzenphysiologie. ii. 

 P. 307. § Physiology of Plants, p. 300. fj Bull. Acad. d. Sc. d St Petersburg, 

 WW, f Op. ciL pp. 332-335. ** Jonrn. Linn. Soc. Dot. vol. 21. 



Jouhnal of Botany.— Vol. 20. [Dec, 1888.] 2 a 



