ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 679 



frequently the function of accumulating water for the future neces- 

 sities of transpiration, and thinks that we have here a notable 

 example of the independent relations of the cause which produces a 

 change in the structure of plants, and the future physiological utility 

 of the anatomical change. 



Structure and Function of the Epidermal Tissue.* — M. Wester- 

 maier treats the structure of the epidermal tissue of plants from three 

 points of view : — 1st, the cuticle ; 2nd, the epidermal system as a 

 system for the supply of water to the plant ; and 3rd, in relation to 

 its protective function. 



The author brings forward evidence, experimental and theoretical, 

 for regarding the epidermal tissue as a system which has for its 

 function the constant maintenance of a supply of water in the plant. 

 This is shown by the rapidity with which water passes from one cell 

 to another in the assimilating tissue, while the epidermal tissue 

 retains it for a much longer period. The aqueous epidermal cells are 

 distinguished by their thin radial walls, which permit the passage of 

 water from cell to cell of this tissue, while confining it within it ; 

 these radial walls are also provided with numerous pores. The 

 constant supply of water to the various parts of the plants is main- 

 tained by a double aqueous system, an inner much branched one, and 

 an outer or epidermal system. 



Protective Sheath and its Strengthenings.f — S. Schwendener 

 enumerates the following as the most important modes by which 

 additional strength is imparted to the protective sheath of the fibro- 

 vascular bundle : — 1. Thickening of the cell-walls of the sheath 

 itself ; this occurs commonly in monocotyledons, rarely in dicoty- 

 ledons ; it has not been observed in gymnosperms or vascular crypto- 

 gams. 2. Thickening of the walls of the adjoining cortical cells, the 

 cells of the sheath itself being thin-walled ; characteristic of ferns. 

 3. Thickening of the walls both of the sheath itself and of the neigh- 

 bouring cortical cells; in Stipa pennata arid capillata, Dasylirion, 

 Poa compressa, Juncus glaucus, &c. 4. Thickening of the cell-walls 

 of the sheath, and of the layers of cells that bound it on the inner 

 side ; at present observed only in Bestio sulcatus. 5. Strengthening 

 of the sheath by addition of bast above the leptome-bundles ; in the 

 root of Lauraceas. 6. Strengthening of the eheath by ridges in the 

 adjoining cortical cells ; the <^-sheaths of Russow. 7. Strengthening 

 of the sheath by a ring of horny parenchyma, separated from the 

 sheath by from two to four layers of thin-walled cortical cells ; in the 

 roots of various Aroidese and Bromeliacese. The author notes that it 

 is a rule without exception that the roots of all plants growing on 

 rocks or on steppes have strongly thickened sheaths. Where the 

 soil in which the plants grow is always soft and moist, no mechanical 

 thickenings are found to the sheath; as in Naias, Pofamogeton, 

 Sparganium, Sagittaria, Alisma, Calla, &c. 



* Pringsheim's Jahrb. Wiss. Bot., xiv. (1883) pp. 43-81 (3 pis.), 

 t Ber. Deutsch. Bot. Gesellsfh., i. (1883) pp. 48-53. 



