ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 263 



Changes in a Rooting Ivy-Leaf.* — M. E. Mer found that an ivy-leaf 

 dipped in water by the free extremity of the petiole produced at that spot 

 a cushion from which roots were developed. Placed then in contact with 

 the soil, the roots increased and fixed themselves, and the root was kept 

 alive for a period of seven years ; there was no production of buds, as in 

 Begonia leaves, to deprive it of its store of food-material. 



During this period great changes took place in the tissues of the leaf. 

 The petiole increased in diameter, as also the lamina in thickness by about 

 one-third. The vascular bundles of the petiole had increased three to four 

 fold in size, but without any development of sclerenchymatous elements. 

 In the lamina, the palisade-tissue had increased to more than one-half the 

 entire thickness of the leaf, the cells increasing greatly in length at right 

 angles to the surface, and then dividing by septa parallel to the surface. 

 This was especially the case with the parenchyma of the upper surface of 

 the leaf. 



Leaves of Grasses.! — Herr M. Giintz has examined the structure of 

 the leaves of 132 species of grass with reference to their habit and mode 

 of life. He finds that, as a rule, xerophilous grasses have erect narrow 

 leaves, often channelled or folded, with strongly thickened cuticle, con- 

 trivances for the protection of the stomata by hairs or a coating of wax, and 

 strongly developed tissue for the retention of water. Hygrophilous grasses, 

 on the other hand, and those which grow in the shade, have usually fiat 

 leaves with only slightly thickened cuticle, free stomata, without any 

 coating of wax, and, except in tropical species, but slender development 

 of the aqueous tissue. The author further classifies, with respect to their 

 habits and the structure of their leaves in four groups, viz. : — (1) Savannah 

 grasses ; (2) Meadow grasses ; (3) Bamboos ; and (4) Steppe grasses. 



Coloured Leaves.^ — From an examination of the anatomical structure of 

 a large number of coloured and variegated leaves, and of the physiological 

 properties of their pigments, Dr. C. Hassack concludes that the white colour 

 in variegated leaves results from the absence of pigment in the tissues, and 

 the presence of numerous interstices filled with air between the cells ; the 

 reflection of light from the numerous air-bubbles in them causes the parts 

 of the leaf which are really colourless to appear white. In leaves with 

 yellow variegation, the normal chlorophyll is replaced by xanthophyll, 

 which colours light-yellow the protoplasm collected into irregular parietal 

 lumps, and occurs also in the form of minute granules. The grey-green, 

 which often appears in coloured leaves in addition to white, is caused by 

 white layers of tissue which lie above the green parts of the cells and 

 partially obscure their colour. Silver-white spots on leaves with a metallic 

 shimmer, are the result of an entire reflection of the light from large 

 shallow air-cavities, which stretch between the colourless and the green 

 layers of tissue in a direction parallel to the surface of the leaf. Eed and 

 brown tints are caused by the presence of anthocyan dissolved in the cell- 

 sap, partly in the epidermis only, partly in the parenchyma only, partly in 

 both tissues. The various tints depend on the intensity of the colour, and 

 the concurrence of red cells with green, yellow, or white portions of tissue. 

 A papillose structure of the epidermis, peculiar trichomes, or, in a few cases, 

 a wavy structure of the entire leaf, is the cause of the velvety sheen of 



* Bull. Soc. Bot. France, viii. (1886) pp. 136-41. 



t Giintz, M., ' Unters. iiber d. anatom. Structur dcr Gramineenblatter,' 70 pp. and 

 2 pis., Leipzig, 1886. See Bot,. Centralbl., xxviii. (1886) p. 201. 



X Bot. Centralbl., xxviii. (1886) pp. 84-5, 116-21, 150-4, 181-6,211-5,243-6,276-9, 

 808-12, 337-41, 373-5, 385-8 (1 pi.). 



