IN VEGETABLE BIOLOGY. 383 
exposure of the protoplasm to favourable, and its minimum 
exposure to unfavourable (positive) grades of illumination? 
This, with the doctrine of tone-lowering by darkness, sectioning 
&c., and that of recovery from mechanical strain, leaves unex- 
plained no photolytie phenomenon with which I am acquainted. 
Some Remarks on Dr. A. F. W. Schimper's Views. 
At the end of a long memoir in Pringsheim's * Jahrbücher für 
wissenschaftliche Botanik ' for 1885, Schimper has some remarks 
upon the movements of chlorophyll, which I regret to have over- 
looked. Repeating the observations of Luders* upon the run-- 
ning together round the nucleus of the chromatophores of 
certain Diatoms in sunlight so as to form a heap in the centre of 
the frustule, and premising that these and other displacements 
of chlorophyll are examples of the irritability aroused in proto- 
plasm by variations in the intensity of light, he thinks that 
strong stimuli of any kind, such as intense light, darkness, 
sectioning, &c., cause the chlorophyll to collect in one or two 
masses, while weaker ones bring about a shifting of it toa wall 
or walls from which it was before absent: the former of these 
corresponding to what I have called “ massed apostrophe "— 
is named by Schimper “ systrophe,” a very convenient word T ; 
the latter answers to epistrophe. But in addition to this * pho- 
totonic ” movement ——movement not governed by the direction of 
light and dependent upon the structure of the organ—there is 
another kind (“ phototactie”) for which the direction of incident 
light is the dominant consideration. It is in accordance with 
the latter that chlorophyll grains, arriving by phototonic action 
upon the side-walls, turn edge-up, and are by this means pro- 
tected from the injurious effects of intense light. An additional 
advantage derived by chlorophyll from epistrophe, apostrophe, or 
systrophe is that its chemical relation to the atmosphere is thereby 
regulated. Access of carbonic acid is a necessary condition of 
assimilation ; but oxygen has a destructive effect on chlorophyll. 
When in epistrophe, therefore, the chlorophyll is exposed as 
much as possible to the access of carbonic acid; but should the 
* Bot. Zeitung, 1862, p. 41, &c. | 
t I cannot agree with Schimper as to the difference between apostrophe and 
Systrophe ; the latter I endeavoured in the previous memoir to connect with 
the former by merely mechanical considerations. 
LINN, JOURN.—BOTANY, VOL. XXIV. 25 
