IN VEGETABLE BIOLOGY. 227 
in four hours, while the countermovement occupied half as many 
days, four hours being about the time taken by ordinary aero- 
phytes to recover from the effects of only a few hours’ withdrawal 
of light. Perusal of the table will make it evident that many 
similar facts could be cited were such a course deemed requisite. 
Fifthly. By the parallelism shown in positive and negative 
apostrophization, clear proof is given that to neither movement 
does welfare of the chlorophyll stand in any necessary relation. 
This has already been spoken of; it will be sufficient here to 
remark that adherents to Bóhm's theory must not only admit 
that insolation is more harmfulto chlorophyll than withdrawal 
oflight; they are bound to maintain that the difference in the 
amount of injury accruing from these two causes is much greater 
in the case of aquatic types than of sun-loving aerophytes, for 
the grains of the former (more readily apostrophized in sunlight) 
take a much longer time over negative apostrophization than do 
those of the latter. 
Sixthly. But, it may be asked, how is it possible to explain 
the massing of chlorophyll upon continued insolation except, as 
Stahl does, by supposing it to be a method whereby the injurious 
effects of strong light are minimized? The fact that massing 
also takes place in darkness, although a good, is scarcely a clinch- 
ing argument against the protection doctrine, since similar 
résults may ensue from dissimilar causes: there can also be no 
doubt that the massed chlorophyll is less exposed to light because 
of the shadow which some of the grains are now able to cast 
upon their neighbours; besides this, it is shown on p. 281 
that massing is the cause of some of the grains being forced upon 
their edge, and so partially withdrawn from the sun's influence. 
If, however, it is possible to refer massing to purely mechanical 
action, it is submitted that the protection doctrine must be aban- 
doned, since the directive effects of light now vanish. Such me- 
chanical considerations are easily reached. Suppose a cell whose 
chlorophyll has just been positively apostrophized. The grains 
now lie uniformly disposed around the cell, and, in virtue of the 
disturbance of the molecular equilibrium induced in protoplasm 
by light, they shift their position, remaining all the while, for 
photometric reasons, upon the lateral walls. This movement 
can be traced in some cases, as e. g. in the marginal cells of Lemna 
irisulca, but the observation is a trying and tedious one ; its 
speed depends on the ratio between the protoplasmic momentum 
