RELATION OF LEAF STRUCTURE TO PHYSICAL FACTORS 35 



to Viola palustris, a shade-mesophyte. The difference between them 

 consists in their respective amounts of palisade tissue, Erodium 

 having two rows and Viola one and a half rows. This indicates 

 that Viola is adapting itself to shade conditions. Saxifraga debilis 

 and Senecio carthamioides with a light value of 0.05 have one and 

 a half rows of palisade cells very loosely arranged. Arnica cordi- 

 folia and Cicuta grayii still show hereditary characteristics in a 

 somewhat thickened upper cuticle and two rows of palisade cells. 

 These latter, however, are evidently in a process of reduction, since 

 the second row is shorter and fewer-celled than the upper. At the 

 same time an adaptation to a moist shady habitat is to be found in 

 the looseness of all tissues. 



HELIOPHYTA (SUNLIGHT PLANTS) 



Brook banks and bogs : light I ; available water 25-58% ; hu- 

 midity 40-70%; temperature 4O-75. 



CLEMENTSIA RHODANTHA : diphotophyll 850 /4 in center, 450 /4 at 

 edges ; epidermis 40 /4 ; cuticle, upper 2 p, lower thin ; chlorenchym 

 (570/4 in center, 370/4 at edges) lacunose chains of prolate cells 

 85 /4, more numerous next to upper epidermis ; central subglobose 

 and oblong cells. (Plate III, fig. 3.) 



Sedum roseum: leaf 750/4 in center. 



Claytonia megarrhiza (alpine rock-cleft; available water 12- 

 17%) : leaf 750/4 in center; epidermis 50/4; smaller central region. 



LILIUM MONTANUM : diphotophyll 400 /4 ; epidermis, upper 40 /4, 

 lower 30/4; cuticle, upper 5/4, lower 3/4; chlorenchym (330/4) I 

 close row prolate and prolobate palisade cells 80/4 (in the propor- 

 tion of i to 2) ; lacunose irregular and star-shaped sponge cells. 

 (Plate III, fig. 4.) 



Anemone globosa (aspens, early spring) : leaf 300/4; lower epi- 

 dermis 40 /4 ; cuticle 5 /4 ; sponge cells closer. 



Dodecatheon pauciflorum: leaf 350/4; upper epidermis 30/4; 

 palisade cells all prolate 75 /4. 



Gentiana frigida (sub-type) : leaf 350/4; epidermis 30/4; chloren- 

 chym (290/4) 2 loose rows prolate palisade cells 40/4; lacunose sub- 

 globose and oblong sponge cells. 



SENECIO CROCATUS : diphotophyll 400 /4 ; epidermis 25 /4 ; cuticle 

 5/4; chlorenchym (350/4) 2 loose rows prolate palisade cells 75/4; 

 lacunose irregular sponge cells. ('Plate III, fig. 5.) 



