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. 



