CURRENT LITERATURE. 63
formation of the fruit, and the author had before been led to the conclusion that growth in thickness took place every night, and might be expected to show itself in about 25 concentric layers. The process and methods now described prove this supposition correct. Owing to the thinness of the wall each layer is only about 04 ft, in thickness, or less than the wave length of yellow light. Hence the necessity for a very considerable swelling of the hair, but with the proper treatment as above the stratification could be seen with a | inch objective.
P. F. F.
Osterhout. W. G. V. Tolerance of fresh water by Marine plants and its relation to adaptation Bot. Gaz. 63; 146-149; 1917.
Osterhout points out " the remarkable differences between marine plants and even between different cells of the same plant with respect to their tolerance of fresh water " and gives an interesting discussion on the theory of adaptation. Polysiphunia violacca is given as an instance where death takes place with great rapidity on transference to fresh water. Various others, representative of the red, brown, green and blue green algae showed extreme tolerance of fresh water. One particular instance is, where, at the mouth of a brook, all kinds of algae were exposed alternately to 6 hours of fresh water and 6 hours of salt water between the tides. Zostera maritima is found 'in places where the roots are constantly in salt water while the leaves are alternately under salt and fresh water. It is found that the roots of this plant die in a few minutes in fresh water. This difference between the roots and leaves is in accordance with the theory of adaptation as the leaves under such conditions will be expected to be more tolerant of fresh water than the roots. But the same differences between roots and leaves are also found in plants of the same species growing constantly in sea water "where no opportunity for adaptation to fresh water occurs." The author remarks " that characters which seem to be tho result of adaptation were in this case present from the beginning and must be ascribed entirely to different causes."
T. E.
Heredity.
Bateson, W., Studies in Variegation— Journal of Genetics Vllt No. 2. {April 1919) pp. 93—98 3 col. pi.
The author draws attention to the two forms of variegation due to deficiency of chlorophyl in (a) the skin a epidermal layer, so that there is a white skin on a green core, and in (b) the middle of a leaf, so ihat there is a green skin over a white core. This last is much less common than the other. Variegated plants of the first kind,: however fertilised, always give white or albino offspring which of course do not live long. The leaves have usually a white edging and green centre. In the second kind the leaves have a green edging and pale centre.
Two instances were noticed of a reversal i.e., of a variegated plant of the kind (a) bearing a shoot of (b). These were in variegated varieties of Euonymus japonicus and Pelargonium.
