PHOTOLYSIS IN LEMNA TR1SULCA. 355 



further explanation ; in estimating the average number of grains 

 per cell fractions, both here and elsewhere, have been omitted. 



No. of No. of cells Total No. Maximum Minimum Average 

 plant. examined. of grains. in a cell. in a cell. per cell. 



I. 12 516 56 34 43 

 II. 12 444 52 26 87 



III. 12 886 46 20 32 



IV. 12 866 52 18 80 

 V. 12 426 44 20 85 



VI. 12 354 36 22 29 



The last three plants upon this table were examined for me by 

 my brother. His total for the 36 cells is 1146, giving an average 

 of 31 grains per cell; mine is just 200 more, which means an 

 average of 37 ; the grand average obtained from both is thus 34, 

 and this may be regarded as approximately correct. 



Cells of the thick part similarly examined by myself alone give 

 the following numbers : — 



No. of No. of cells Total No. Maximum Minimum Averago 

 plant. examined. of grains. in a cell. in a cell. per cell. 



I. 12 423 40 80 35 



II. 12 442 62 34 45 

 III. 12 696 62 38 49 



That is, 36 cells yield a total of 1561 grains, or an average of 43 

 per cell. 



The two following tables refer to plants set overnight in dark- 

 ness ; as inspection will immediately show, 1 am uuable to bear 

 out Scliimper's before -mentioned statement that the superficial 

 wall abutting on the epidermis is deprived of chlorophyll as the 

 result of one night's darkness. In these cases the grams upon the 

 lower wall were counted, after focussing through the upper wall ; 

 and no difficulty was met with in the course of this. The upper 

 three columns deal with upper, the lower three with under walls. 

 The first table refers to marginal cells. 



Total No. of , 



No. of No. of cells grains still in Maximum in Minimum in 

 plant. examined. epistrophe. epistrophe. epistrophe. 



I. 12 50 7 



II. 12 69 9 2 



III. 12 103 12 6 



I. 12 46 6 



II. 12 87 11 J 

 III. 12 91 9 6 



This gives a total of 222 for the 36 upper, and 224 for the lower 

 surface-walls, or an average of 6 per wall, which is equivalent to 

 12 grains per cell. Consequently the effect of night is to tnuufer to 



the mle-uali* only 22 of the 34 grain* of a nil, leaving 12 o) thru, Mil! 

 in e^lropke, and I f< 1 convinced that this is a COM ct statement so 



far as refers to healthy cells, a repn -dilation of one night 8 darkness 



2 a 2 



