ZOOLOGY AND BOTANY, MIOROSOOPY, ETC. 109 



fourth of what it was at the early stage of growth. The leaves of B. acetosa 

 are very rich in nitrogenous substances, and are the principal seat of the 

 formation of oxalic acid and of the destruction of the nitrates. 



Amaranthus caudatus contains a considerable proportion of nitrates, and 

 the oxalic acid is mainly in an insoluble form. At the commencement of 

 flowering (June 18th) the percentage of oxalic acid was 5-86. 



Clienopodium quinoa yields a neutral juice which is almost free from 

 nitrates, but contains a relatively large proportion of soluble oxalates. In 

 the early stage of growth (May 18th) the percentage of oxalic acid was 

 3 • 9, and the bases in the ash (25 • 6 per cent.) were far more than sufficient 

 to neutralize the whole of the acid. 



Mesembryanthemum cri/stallinum. — The seed does not contain oxalic 

 acid. In the early stage of growth (June 9th) a considerable quantity of 

 oxalic acid is formed, a part being in the soluble form. As growth pro- 

 ceeds the juice becomes acid, and at a later stage, when the flowers begin 

 to open, it becomes neutral in the root, but is acid in the stalks and leaves. 



(4) Structure of Tissues. 



Assimilating System.* — Dr. G. Haberlandt contests the theory of 

 Stahl that the factor which exercises the greatest influence on the structure 

 of the assimilating system of plants, and especially on the palisade- 

 parenchyma of leaves, is the intensity of light. His view is rather that it 

 is governed chiefly by the facility which it affords for the conduction of 

 the food-materials. Although in the great majority of cases the statement 

 of Stahl is correct, that in the palisade-cells the chlorophyll-grains take 

 up their epistrophic or apostrophic position according to the direction 

 and intensity of the light, yet it can be shown, especially in those instances 

 where the walls of these cells are curved or oblique, that the determining 

 influence is the anatomical structure of the walls themselves. Those cell- 

 walls through which the current of food-material passes, or a regular 

 metastasis takes place, are free of chlorophyll-grains. 



The theory that the oblique position of palisade-cells is a direct 

 contrivance for the transmission of light, is contradicted by the fact that 

 it occurs in conditions where light is entirely excluded, as in leaves 

 inclosed within buds or even buried in the ground. Evergreen leaves, even 

 when growing in the shade, contain an abundant palisade-parenchyma. 

 The author regards the influence of light on the greater or less development 

 of the assimilating system as simply an example of irritation which has 

 become hereditary ; and where this inherited tendency to a copious develop- 

 ment of the assimilating tissue is wanting, even the most intense illumina- 

 tion is powerless to produce it. 



The principles of the structure of the assimilating tissue, on the 

 above theory, are explained in detail; and it is pointed out that the 

 arrangement best adapted for the assimilating cells to carry out their 

 function is when they are placed radially round the vascular bundles. 



Vascular Bundles of Zea Mays.j — Herr H. Potonie describes the de- 

 velopment of the small anastomoses which, in the leaves of the maize, 

 connect the principal longitudinal vascular bundles transversely with one 

 another, and points out the singular fact that the conducting tissue repre- 

 sented by the parenchyma-sheath of these anastomoses is of the same 

 origin as the elements of the anastomosing bundles themselves, and differs 

 in origin from the parenchyma-sheaths of the principal bundles, which are 

 of a similar value from a physiological point of view. 



* Ber. Deutsch. Bot. Gesell., iv. (1886) pp. 206-36 (1 pL). t Ibid., pp. 110-2 (1 fig.). 



