864 MR. 8. LE M. MOORK'S STUDIES 
with one exception, all other practice in favour of simple sec- 
tions with the razor, taking care not to make the section too thin 
. and thereby destroy the cells. Thus prepared, cells may be 
mounted in water rapidly ; and for some time they will retain 
their vitality and betray no change in the position of and no 
injury to the chlorophyll. The exception is where, in examining 
the lowest mesophyll layer, this can be detached without injury 
along with its epidermis by simply tearing off pieces of the latter. 
The only two species admitting of this treatment are, as far as I 
have hitherto found, Viola odorata and (much less favourably) 
Ozalis Acetosella: these are both shade-lovers ; could a similarly 
behaving sun-lover be discovered, the photolytic differences 
between the two groups could be demonstrated to a whole class 
within a few minutes. 
The “Activity or Passivity” Question. 
The behaviour of the chlorophyll of epidermal cells in the 
sun's rays and in darkness throws a great deal of light upon the 
vexed question of the activity or passivity of the chlorophyll 
grains in photolysis. During the past summer I have bad 
many opportunities of studying the epidermal chlorophyll of 
insolated leaves attached to or detached from the parent, and 
either free in the air or covered with a glass slide under water 
frequently renewed. In almost all cases '— Viola odorata, t Circe 
Lutetiana, Chrysanthemum Matricaria, C. segetum, Pyrethrum 
Parthenium, * Bellis perennis, Achillea Millefolium, 0 Heli- 
anthus tuberosus, *Solanum Dulcamara, *S. tuberosum, OAna- 
gallis arvensis, t Mercurialis annua, among others—no change 
was observed in the position of the grains even after several 
hours' direct sunlight—that is, long after apostrophe had set in 
in the deeper cells; and even in the epidermis of Hydrocharis 
Morsus-rane no tendency to apostrophe was detected after seven 
hours’ insolation. Occasionally a cell might be met with in 
which a few, very rarely all, of its grains were found upon the 
side-walls ; but so seldom is this seen, that it may well be ques 
tioned whether positive apostrophe is really a contingency in the 
history of epidermal chlorophyll. Similarly, in darkness the grains 
! The names marked with an * are those of plants of which the epidermal 
chlorophyll contains starch; the t is prefixed to species with but slight 
traces ; and the 0 to those with no trace of starch in the chloroplasts of their 
epidermal cells, 
