IN VEGETABLE BIOLOGY. 221 
(an objection applying equally to Bóhm's view), this doctrine 
also gives no explanation of the dependence of the positive critical 
point upon species, individual, and cell. Can it be that this sup- 
posed injurious accumulation commences in aquatic plants at 
grades of illumination far lower than those necessary to produce 
the same effects in sun-loving types? If so, where are the ex- 
periments which render this doctrine probable? And if there 
are none (and I know of none), does not Stahl lay himself open 
to precisely the same objection which he finds to Böhm? Nor 
is this all. If the grains are apostrophized in order to prevent 
some supposed injury which it is in the capacity of light to in- 
flict upon them, why do they assume precisely the same position 
in darkness, 7. e. under circumstances rendering injury by light 
impossible? If Stahl's view be retained, we can only account 
for the facts of negative apostrophe by sinning against the New- 
tonian injunction with reference to the multiplication of causes. 
Before doing this, let us see whether there is not a simpler 
theory capable of accounting for the facts not only of positive 
but also of negative apostrophe. 
It is admitted on all hands that the prime agent in the varia- 
tions in position undergone by chlorophyll is the protoplasm of 
the cell, authors differing only as to whether this is the sole 
cause or whether the grains themselves be not to a slight extent 
contributory. For present purposes the latter question may be 
overlooked. It is therefore obvious that, when epistrophe sets 
in, the tendency of the protoplasm is to collect upon the super- 
ficial walls, the grains being carried out from the side-walls ia 
consequence. But when, as the result of insolating leaves of 
Funaria, for instance, the grains move to the side-walls, this 
happens because a reverse condition is set up, the protoplasm 
now tending to move away to the least highly illuminated por- 
tions of the cell. The fundamental mistake made by Bohm and 
Stahl is in ignoring in their respective theories this attracting 
and repelling action of light upon protoplasm. The researches 
of Famintzin, Cohn, Schmidt, Stahl, and especially Strasburger 
have taught that light has great influence on the movements of 
zoospores. Strasburger*, it wil be remembered, finds that 
zoospores whose movements are affected by light (called by him 
* phototactic ") are either “ aphotometric,” that is move uni- 
* Jenaische Zeitschrift, 1878. The bibliography of the subject will be found 
there. 
