AGRICULTURAL BOTANY. 631 



portatiou or assimilation products, wbicti is said to be more active during ttie 

 hours of dayligtit. 



Chang'es in the osmotic pressure of the sap of the leaves of various plants, 

 H. H. Dixon and W. R. G. Atkins {Sci. Proc. Roy. Dublin Soc, n. ser., IS 

 (1912), Nos. 16, pp. 210^22; IS, pp. 229-238, figs. 2; 19, pp. 239-2^6, fig. i).— In- 

 vestigations have been made on the changes in the osmotic pressure of the sap 

 of the leaves, the method employed being that described elsewhere (E. S. R., 

 23, p. 526). 



Experiments with Syringa v^ulgaris were carried on to trace the changes 

 in the osmotic pressure during the unfolding of the buds and the maturing of 

 the leaves. It was found that the osmotic pressure of the sap of the buds 

 rose from February to March, and this is attributed to the transportation of 

 dissolved substances into the buds and to the solution of previously undissolved 

 bodies in them. In April the rapid increase in size of the leaves was asso- 

 ciated with a dilution of the sap, indicating that during this period the ab- 

 sorption of water predominated over the accumulation of dissolved substances. 

 From that time on, as the leaves grew and matured, the pressure continued 

 to rise until June, when the observations were brought to a close. Previous 

 observations, however, indicate that the pressure continues to rise in the leaves 

 during the summer. After the final rise of osmotic pressure in the late sum- 

 mer a diminution is registered in the sap from the leaves just about to fall. 

 This is attributed to the transportation of materials from the leaves. 



In the second and third papers the materials selected for investigation were 

 the leaves of evergreen plants. In Ilex aquifoUum there was not only a differ- 

 ence observable between the mature and immature leaves in their osmotic 

 pressure, but also between mature leaves of various ages. 



With Heclera helix the effect of direct sunlight on osmotic pressure was In- 

 vestigated, and with this plant it was also found that the age of the leaves had 

 a marked influence on the concentration of the cell sap. Leaves of the ivy 

 which were grown in a southern aspect had a consistently higher cryoscopie 

 value than those of leaves gi'own in a northern aspect. This confirms other 

 observations which showed that the depression of freezing point of the sap 

 of the aerial portions of plants was greater in plants grown in a sunny position 

 than in those grown in more shaded situations. In Hedera as in l\e:x the de- 

 pressions in the curve seemed to corresiiond to periods of elongation of the 

 shoots and the formation of new leaves, and it was found impossible to corre- 

 late the form of the curves closely with external conditions. The effect of 

 photosynthesis on variation in osmotic pressure was investigated, and the re- 

 sults indicate that photosynthesis is active in raising the concentration. 



The formation of mechanical tissue as influenced by tension and contact, 

 W. D. Brush {Bot. Gas., 53 (.1912), No. 6, i)p. 453-Jf77, figs. S).— Studies are 

 reported on the formation of mechanical tissue in the tendrils of Passiflora 

 cm-ulea as influenced by tension and contact. The experiments were conducted 

 in the greenhouse under control conditions and the results are given in detail. 



It was found that The tendrils which function to support the plant possess 

 a greater breaking strength than those which have gi'asped no support. The 

 cause of this greatly increased strength is attributed to a combination of the 

 two factors contact and tension. Comparing the values of these two factors, 

 the author concludes that contact plays the more important part, though the 

 strength of the tendril may be still more increased by the factor of tension. 

 The author claims that tension may also act as a stimulus and thereby result 

 in the production of stronger tissues in the plant. It is thought probable that 

 this increased growth is due to increased hydrostatic pressure. 



A bibliography is appended. 



