68 SUMMAKY OF CURRENT RESEARCHES RELATING TO 



of the form of any particular part of a plant to the individual cells, 

 so that the individual cell plays a prominent part, and the behaviour 

 of these determines the form of the organ. A different view is held 

 by Hofmeister, Sachs, De Bary, and Hanstein, who regard as the 

 primary fact the form of the organ itself, which then determines the 

 form and mode of division of the cells. An intermediate position 

 between the two is held by Schwendener; the arrangement of the 

 cells and the directions of the dividing walls being, according to him, 

 determined by two variable factors : — (1) by the individuality of the 

 cell; (2) by the form or complete growth of the entire organ, to 

 which Schwendener also attributes a share in the arrangement and 

 growth of cells. The final position of the walls and arrangement of 

 the cells is often also influenced by pressure. 



In order to determine the relative energies of growth of the cells 

 of the apical region, the author proposes the following theoretical 

 considerations : — 



1. "The apical cell displays the same activity with regard to 

 increase in volume during successive stages." By a stage the author 

 means the time which elapses between the formation of a division- 

 wall in the apical cell and the formation of the next following 

 division-wall. 



2. " The successive segments display an equal activity with 

 regard to increase in volume during successive stages." In this con- 

 nection the relationship is investigated between the volume and the 

 projection of the lateral profile of a triangular pyramidal and of a 

 two-edged apical cell. 



After these theoretical propositions, a comparison is made of the 

 energy of growth of the apical cell in Didyota (according to Naegeli), 

 Hypoglossum Lejprieurii (Naegeli), Metzgeria furcata (Goebel), Salvinia 

 natans (Pringsheim), Equisetum arvense (Cramer), E. scirpoides (Reess), 

 and Selaginella Martensii (Pfeffer). 



The general result is stated as follows : — The maximum of 

 increase in volume lies in general either in the apical cell itself or in 

 the youngest segments. If we look only at the region which in- 

 cludes the apical cell and the four youngest segments, in none of the 

 cases mentioned above is the increase of volume least in the apical 

 cell. 



Action of Nitrous Oxide on Vegetable Cells.*— Prof. W. Detmer 

 has tried a series of experiments on the influence on vegetable tissues 

 of nitrous oxide gas, which he states may, to a certain extent, replace 

 oxygen in the respiration of plants. For this purpose he took pains 

 to obtain the gas absolutely pure, and carefully to exclude every trace 

 of atmospheric air. The main results of his experiments, made on 

 Triticum vulgare and Pisum sativum, are as follows : — 



1. When grains of wheat or peas are made to swell in water which 

 has been boiled and allowed to cool, and then placed for a considerable 

 time in contact with pure nitrous oxide, they lose their power of 

 germination. 



* SB. Jenaisch. Ges. Med. u. Naturwisa., 1881, July 1. See Bot. Ztg., xxxix. 

 (1881) p. 677. 



