Appendix. 



selves in planes parallel to the surface of the leaf, thus exposing 

 as much of their surface as possible to the action of light, but 

 when exposed to the action of direct sunlight, arrange them- 

 selves around the side-walls of the cells, thus presenting a less 

 amount of their surface to the intense light. 



It may be added that at the date of writing, March 29th, 

 over three weeks after the observations above recorded were 

 made, an examination was made of the leaves of the same moss, 

 which had been left in a faintly lighted closet since the former 

 date, without care of any kind. All the leaves examined were 

 found to have their chlorophyll grains arranged in planes parallel 

 to the leaf surface, thus showing that after removal from the sun- 

 light these bodies had again arranged themselves in their former 

 position. 



If .^ of an inch be taken as the diameter of an ordinary 

 cell and this is a rather large measurement for this species it 

 will be seen that chlorophyll bodies pass through a very small 

 space in performing their migrations to and from the cell-walls. 

 Supposing one of the chlorophyll bodies to be exactly in the middle 

 of the cell, it cannot pass through more than r -Vo of an inch before 

 reaching the cell-walls. At this rate, then, about a year will be 

 consumed in traveling a single inch. Still it is pleasant to think 

 that the mites who chance to be born in a moss-cell have travel- 

 ing facilities which, though a trifle slow, are, nevertheless, safe 

 and regular. 



