IN VEGETABLE BIOLOGY. 235 
tive apostrophe from epistrophe than vice versd, but the assump- 
tion of epistrophe from positive apostrophe is slower than that of 
positive apostrophe from epistrophe. Moreover, it always takes 
less time to bring about positive apostrophe from epistrophe than 
epistrophe from negative apostrophe, and epistrophe from posi- 
tive apostrophe than negative apostrophe from epistrophe. This 
may be expressed in a general way by saying that as an advance 
is made towards the positive end of the photrum, the correspond- 
ing movement of the chlorophyll is performed with more despatch, 
while the reverse is the case in proceeding towards the negative 
end. This it is proposed to call the “Law of Positive Pro- 
gression.” 
The accompanying Table (p. 234) contains all the information 
upon this subject I have been able to collect. It will be seen that 
three classes of types are included, viz. aquatics, shade-loving 
aerophytes, and ordinary plants. Compared with these last, 
aquatics require a relatively enormous period to fulfil the condi- 
tion expressed in column 1, and in this point shade-lovers greatly 
resemble aquatics. The same may be said for column 2, but the 
difference here is less. With regard to column 3, had sunlight 
of good quality been used for inducing apostrophe in the aquatic 
types, the times in their cases would have been much shorter 
than those required by the rest; but it was thought advisable 
not to use the highest light with them, in order the more dis- 
tinctly to emphasize the Law. The reason for the large intervals 
of time which appear in the lower part of the Table is that the 
determinations were made on the short November days, when, 
until nearly noon, the chlorophyll is imperfectly epistrophized*, 
and microscopic examination is practicable only for a few hours 
thereafter. It should be added that care was taken to eliminate 
heating effects by the frequent pouring of cold water over plants 
whose chlorophyll was in process of positive apostrophization. 
Some Points in the Rotation of the Protoplasm of Elodea and 
Vallisneria. 
In speaking of photolysis in Elodea, it was poiuted out that 
the chlorophyll of the upper is more readily apostrophized than 
that of the lower layer of cells ; the same thing is to be said with 
respect to rotation f. It matters not in what position a leaf be 
* Sometimes on dark days the grains do not move into epistrophe at all. 
t This is noticed by Frank (J. c. p. 240). 
