LE M 
IN VEGETABLE BIOLOGY. 207 
by simply focusing through the overlying epidermis, the air 
having been previously removed from the preparation by gentle 
pressure upon the cover-slip *. 
The negative apostrophe of angiospermous chlorophyll may be 
well studied in seedling and adult plants of Eschscholtzia califor- 
nica. If one of these be placed in darkness overnight, on cutting 
off a leaf-lobe in the morning and mounting it in water lower 
side up, by focusing through the epidermis it can easily be seen 
that the chlorophyll of the lower layer of mesophyll-cells which 
bad, on the previous day, been uniformly or nearly uniformly 
distributed upon the walls lying, in the rough sense, in the plane 
of the leaf (Pl. VII. fig. 1), is now collected in dense masses in the 
corners of the cells, occupying exactly the position assumed after 
the prolonged action of sunlight (fig. 2). So closely are the grains 
packed that, but for their colour, the masses might be mistaken 
for local thickenings of the wall, the fact of their being composed of 
a number of similar small bodies being evident only upon occasion. 
It would appear that the whole night is not required for these 
grains to apostrophize; from the list drawn up on p. 234 it will 
be seen that although apostrophe takes more than six hours it is 
completed in much less than eighteen, by which time the grains 
have become massed, massing being always the result of prolonged 
exposure either to sunlight or to darkness. 
Other sun-loving aerophytes were subjected to the same treat- 
ment with the same result, except that the massing of the grains 
usually makes a moretardy appearance. In the stellate mesophyll- 
cells on either side of the midrib of the involucral scales of the 
garden Chrysanthemum, as in thestipules of Vicia Faba, massing has 
commenced and may be well established after twenty-four hours’ 
darkness ; double that time was found requisite for the mesophyll 
of the primordial leaves of Nigella damascena, while it was only 
after a week in the dark that the mesophyll of Centranthus ruber 
and the cells of the small outer involucral scales of Senecio vul- 
garis had their grains in massed apostrophe, although in all 
these cases simple negative apostrophe is (as the table on p. 234 
shows) induced as readily as in ‚Eschscholtzia itself. But when 
we come to study shade-loving types, we see a great difference. 
If Oxalis Acetosella be set in the dark, the mesophyll of its 
leaflets may be examined day by day without detection of any 
* Removal of the air with the air-pump has been recommended, but this is 
quite unnecessary, 
