532 SUMMARY OF CUREENT RESEARCHES RELATING TO 



upward streaming was observed. Similar results were obtained with 

 Mimulus moschatus. 



The author regaids the viscosity of the plasma as of primary import- 

 ance in this streaming, and believes that, possibly, movement results 

 from the attraction of gravity acting upon the living substance of the 

 plant-cell. The upward streaming noticed in the first experiments 

 appears to be due to the wounding of the tissues. 



Plasma-membrane as "Ultrafilter." * — W. Ruhland has experi- 

 mented with various colouring matters, and is of the opinion that the 

 chief factor governing their absorption through a membrane is the 

 mobihty of the particles. The size of the particles in one and the same 

 colloid solution is very different, so that sometimes the smaller and not 

 the larger particles are absorbed, but the presence of acids, bases, or 

 salts may greatly increase the number of particles absorbed. It would 

 thus seem that the plasma-membrane of cells acts as an " Ultrafilter " in 

 Bechhold's sense. Another important factor governing absorption is the 

 form of the particles ; thus, particles which are quickly absorljed in the 

 free state, pass through much more slowly when in contact with a colloid 

 substance. This seems to point to a colloid nature in the plasma- 

 membrane. The absorption-constant for plant-cells is much smaller 

 than for animal-cells, but it is at pi esent uncertain whether this is due 

 to any inherent differences, although the behaviour towards highly dis- 

 sociated inorganic salts seems to favour this view. 



Improved Iodine-test. t — F. "W. Neger has applied Mohsch's infil- 

 tration-test to the stomata of Conifer needles, and is quite unable to 

 obtain a successful result, but attributes this to the protection of the 

 stomata by deposits of wax ; the author's experiments have led, however, 

 to the discovery of a useful modification of Sach's experiment. When 

 ether (alcohol, etc.) containing a small quantity of dissolved iodine is 

 placed on the under side of foliage-leaves, diffusion takes place through 

 the open stomata, and the presence of starch is made evident by a deep 

 black coloration of the mesophyll, which is evident to the naked eye, 

 even at some distance. The best results are obtained with fully developed 

 and turgescent leaves ; if the leaves are still growing, little or no result 

 is observed, as the starch appears to be immediately used up in the 

 formation of new tissues. 



Structure and Development. 

 Veg-etative. 



Stomata of Palm-leaves. :{: — K. Rudolph has studied the stomatal 

 openings of a large number of palms, and concludes that they are all 

 based upon a single original plan, but that the individual parts are greatly 

 modified in the various species, in accordance with changes of function 



* Ber. Deutsch. Bot. Gesell., xxx. (1912) pp. 139-41. 



t Ber. Deutsch. Bot. Gesell , xxx. (1912) pp. 93-96. 



% SB. Akad. Wiss. Wien, cxx. (1911) pp. 1049-86 (2 pis. and 10 figs.). 



