T. Holm — Chionophila Benth. 37 



is smooth on the dorsal. Viewed ^^en face'' the lateral 

 cell-walls of epidermis are, on both faces, straight, quite 

 thick and porous, especially on the dorsal face; the 

 stomata {-Q-g. 8) are free, and surrounded by mostly four 

 ordinary epidermis-cells. In cross-sections the structure 

 of the cuticle is readily visible {-B.g. 10), and the outer cell- 

 wall of epidermis appears quite thick. The chlorenchyma 

 consists of four layers of palisade-cells, which cover a 

 very open pneumatic tissue of about eight strata. In the 

 marginal portion of the leaf the palisade-tissue extends 

 to the dorsal part of the blade and there is no mechanical 

 tissue neither stereome nor collenchyma in any part of the 

 leaf. The mestome-strands are collateral, all single, and 

 surrounded by green parenchyma sheaths. The leaf- 

 structure is thus approximately isolateral on account of 

 the distribution of the stomata, but not with reference to 

 the structure of the chlorenchyma. The leaf-structure 

 thus resembles that of the high alpine Claytonia megar- 

 rhiza," as far as concerns the distribution of the stomata 

 on both faces of the blade, the several strata of palisade- 

 cells, the thick cuticle and thickwalled epidermis. Bon- 

 nier^ and Wagner^ have offered some interesting contribu- 

 tions to the knowledge of the structure of alpine plants, 

 and according to these authors the leaf-structure of Chion- 

 ophila and of Claytonia megarrhiza appears to be the 

 typical one, which characterizes the overwintering leaves 

 of alpine species. And the highly developed assimilating 

 tissue is in correlation with the pronounced intensity of 

 light at the higher elevations, the considerable decrease of 

 carbonic acid in the atmosphere, beside the very short 

 time of vegetation. At the same time these winter-green 

 leaves are protected against too excessive transpiration 

 during the period of the melting of the snow, by means of 

 the very thick cuticle and pronounced thickening of the 

 cell-walls of epidermis. However, only the leaf has been 

 studied by these authors and the Monocotyledones have, 



'Holm, Theo. Claytonia Gronov, Mem. Natl. Acad, of Sc, vol. 10, 

 Washington. 



* Bonnier, G. -Cultm'es experimentales dans les liautes altitudes, (Comptes 

 Rend. Aead. Sc, 1890). 



Bonnier, G. Influence des liautes altitudes sur les fonctions des vege- 

 taux, (ibid. 1890). 



Bonnier, G. Etude experimentale sur 1 'influence du climat alpin sur la 

 vegetation et les fonctions des plantes, (Bull. Soc. Bot. de France, 1888). 



^ Wagner, A. Zur Kenntniss des Blattbaues der Alpenflauzen und dessen 

 biologischer Bedeutung, (Sitzungsber. Akad. Wiss. Wien, Math. nat. 

 classe, May, 1892). 



