'zoology and botany, microscopy, etc. 95 



same purpose is also answered in other cases by the greater closeness 

 of the network of the vascular bundles, and by the increase in the 

 diameter of the separate bundles. 



Relative Resisting-power of the Upper and Under Surfaces of 

 Leaves.* — Herr L. Kny finds that where the interstices between the 

 finer veins on the upper surface of the leaf are strongly convex, the 

 leaf offers much greater resistance to the tearing force of heavy 

 bodies like shot falling on it, than the lower surface does. But where 

 the upper surface is quite flat, the resisting-power of the two surfaces 

 of the leaf is nearly the same. 



^ Protection of Leaves against the Mechanical Action of Rain and 

 Hail.j — Herr L. Kny considers that a contrivance for this purpose 

 is to be recognized in the rounded swellings of the fundamental tissue 

 of the leaf between the finer veins, such as occurs in Primula elatior, 

 Ballota nigra, Mentha piperita, &c. By this contrivance, the shock of 

 the impact is partially carried from the cells which first receive it 

 to the neighbouring ones, and thence to the fibro-vascular skeleton. 

 This arrangement is not found in leaves which are otherwise protected 

 against this injurious agency, as those which are finely divided, or 

 which are submerged, or have a very thick cuticle, or are sensitive. 



Development of the Stomata of the Oat.^ — Miss E. A. Southworth 

 states that the epidermis of the oat is composed, in the young leaf, 

 before the appearance of the stomata, of quadi-angular cells which 

 afterwards grow much faster in length ; the mother-cell of a stoma 

 being cut off from the end of one of these. On each side of this 

 mother-cell a nearly semicircular accessory cell is cut off out of the 

 adjacent cell, and the mother-cell of the stoma subsequently divides 

 into the two guard-cells. The behaviour of the protoplasm, with 

 which both mother-cell and accessory cells are well filled, is very 

 characteristic. When division takes place, this has condensed in the 

 centre of each cell, so that it appears to be in a continuous band 

 across all four cells. In the immature stoma the protoplasm is very 

 slightly granular, and has a slight green tinge ; when the stoma is 

 mature, the protoplasm appears perfectly homogeneous, and small 

 chlorophyll-bodies containing starch occuj)y the former vacuoles. 



Contents of Sieve-tubes.§ — Herr G. Kraus finds the composition 

 of the sieve-tubes of Cucurhita to differ in different individuals, and even 

 in different parts of the same individual. The proportion of solid 

 contentsisalwaysconsiderable, varying, in small fruits, between 7 and 

 8 per cent., in larger fruits between 9 and 10, or amounting even to 

 14 per cent. The sap that flows out first is usually more concentrated 

 than the later. Of the residue which remains on evaporation, about 

 two-thirds is again soluble in water. A large proportion of the 

 insoluble portion consists of albuminoids. There is also a large 

 amount of non-albuminoid soluble nitrogenous constituents, consisting 



* Ber. Deutsch. Bot. Gesell., iii. (1885) pp. 258-73, f Ibid., pp. 207-13. 

 t Amer. Naturalist, xix. (1885) pp. 710-1 (1 pi.). 



§ Ber. Sitz. Naturf. Gesell. Halle, 1884, pp. 9-14. Cf. this Journal, iv. 

 (1884) p. 586. 



