356 PHOTOLYSIS IN LEMXA TRISULCA. 



upon which will be found at fig. 1 of Tab. 185. If the cells be old, 

 or lie in the neighbourhood of parts which have been injured, apos- 

 trophe will, of course, be much more pronounced, as will appear on 

 reference to Fig. 2, which is an attempt to show the result of one 

 night' 8 darkness upon two such cells ; but even here one or more of 

 the grains are almost always still in epistrophe in the morning. It 

 is significant that, of the 36 cells dealt with in the last table, only 

 one verified the dictum of Stahl by having all its grains in apo- 

 strophe. 



In the next table, cells from the thick part are similarly dealt 

 with : — 



Total No. of 

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



plant. examined. epistrophe. epistrophe. epistrophe. 



I. 12 138 18 9 



II. 12 121 15 6 



HI. 12 119 1G 7 



I- 12 142 18 9 



II- 12 122 17 7 



HI. 12 105 13 6 



From this we gather that 36 upper (outer) walls had between 

 them 378, and a similar number of lower (inner) walls 369 grains 

 still in epistrophe, in spite of their exposure to the night's dark- 

 ness. This gives an average of 10 grains per wall or 20 per cell ; 

 and since the average number of grains in these cells was found to 



be 43, it appears that during the night rather more than 50 per cent, 

 more on to the side walls, the remainder being fairly equally distributed 



upon both upper and lower walls. For 'this condition the term 

 « ' merostrophe "may perhaps be approved . 



It is maintained therefore that photolytic effects are approxi- 

 mately the same in all the ct lis of L. trisulca. In poorish diffused 

 light the grains collect upon the two walls lying parallel to the 

 plane of the frond, to pass in stronger illumination on to the 

 lateral walls, and mass under the influence of still intenser light 

 in the cells' corners. Slow movement towards the side walls 



is caused by darkness ; but in accordance with the rule as to 

 aquatics 



siaerable lapse of time. These four statements are diagram- 

 matically illustrated in figs. 8—6. 



To show the slow rate at which negative apostrophe proceeds, 

 we counted the number of grains still in epistrophe after four days 

 in darkness. My brother found upon the upper wall of 12 

 marginal cells of each of three plants 48, 24 and 23 grains, and on 

 the corresponding lower walls 56, 45 and 48— an average of 6 per 

 ceil; my own figures were 61, 42 and 51 upon the upper, and 

 56, 41 and 36 upon the under walls, or just 8 per cell. Striking 

 the balance between these computations, we find 7 out of 34 grams 

 —or more tlian 20 per cent. ' ' L — ,: "" ;| — *" KV the 



by the 

 in 



•—or more than 20 per cent.— not yet apostrophised, even by 1 

 close of the fourth day. I counted the still epistrophised grains 

 12 cells of the thick part of three plants under similar circum- 

 stances, and got an average of 9 grains per cell, while my brothers 



