592 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Measurement of Turgidity.* — H. de Vries applies the term 

 " isotonic concentration " to the degree of concentration of different 

 solutions in which they attract water with equal force. The strength 

 of a solution of potassium nitrate, which has the same affinity to water 

 as the solution to be examined of any other substance, is termed the 

 " nitre-value " of that substance. Representing the attractive force 

 of a solution of potassium nitrate at 3, the numbers 2, 3, 4, or 5 

 might express that of other solutions. These numbers, representing 

 the attractive force for water of a molecule of the substance in ques- 

 tion in a dilute aqueous solution, are the isotonic coefficients of the 

 different substances. 



The author describes in detail three methods of determining the 

 isotonic coefficients of a substance : — (1) The plasmolytic method, by 

 placing as similar pieces as possible of the tissue in solutions of 

 different concentration of the substance in question and of potassium 

 nitrate, and observing the degree to which the parietal protoplasm is 

 detached from the cell- wall. This method can be applied in the case 

 of only a few plants. (2) The method of plasmolytic transport : by 

 measuring under the camera the plasmolysis which occurs on placing 

 the preparation in a solution of a salt which causes moderate plasmo- 

 lysis; then transferring to solutions of different concentration of 

 other salts, and again observing the plasmolysis. (3) The method by 

 tension of tissue, by observing the curvature of split terminal por- 

 tions of shoots in concentrated solutions of the substance to be 

 examined. 



By turgidity the author understands the affinity of the dissolved 

 substance for water, and gives detailed results as to the proportion 

 of the turgidity due to the different constituents of the cell-sap, the 

 most important of these in this connection being sugar, oxalic acid, 

 and malic acid. Since the turgidity is constantly being changed by 

 substances out of which protoplasm is developed, the inquiry is one 

 of great importance in vegetable physiology. As a general rule, the 

 author finds the isotonic coefficients nearly to correspond for members 

 of the same chemical group. 



B. CRYPTOGAMIA. 



Cxyptogara.ia Vascularia. 



Origin of Roots in Ferns. f — Lachmann has studied the cauline 

 fibrovascular system of the ascending rhizome of Aspidium Filix-mas, 

 which forms a network of hexagonal meshes, from the periphery of 

 which spring the foliar and radical bundles. The former are from 

 five to seven in number, one, medio-dorsal, springing from the bottom 

 of the network, the others inserted symmetrically on its borders. 



* Priagsheim's Jahrb. f. Wiss. Bot., xiv. (1884) pp. 427-601 ; also Vers. Med. 

 K, Akad. Wetensch. Natuiuk., xix. (1883) pp. 314-27. 8ee Bot. Centralbl,, 

 xvii. (1884) p. 170. 



t Comptes Eendus, xcviii. (1884) pp. 833-5. 



