38 EDITH SCHWARTZ CLEMENTS 



Compared with shade-mesophytes, sun-mesophytes show a greater 

 development of palisade tissue either in compactness of the cells, or 

 an increase in length of cell or number of rows. Since for the two 

 groups, the chief difference in the habitat is that of light, it is plain 

 that light must be the most directly concerned with the palisading 

 of the leaf. It is also noticeable that within the sciophytes as a 

 group there is a definite relation between the amount of soil-water 

 and the sponge tissue, the latter increasing in looseness as the former 

 increases in amount. A third fact suggested by *a comparative 

 study of the group is that of the stability of composites. Senecio 

 pudicus, though a shade-plant, has the structure of a heliophyte. 

 The leaves of the Agoseris aurantiaca group, which are all com- 

 posites, have the structure of vertically placed rather xerophytic 

 leaves. They have adapted themselves, however, to considerable 

 water in the soil, by loose tissues, and Senecio chloranthns has rudi- 

 mentary sponge cells. This, on the other hand, has not taken place 

 among the erigerons : E. minor, E. subtrinervis, and E. conspicuus, 

 which, though living in 20-25% of soil-water, can scarcely be dis- 

 tinguished from E. speciosus and Aster geyeri in a xerophytic group 

 with considerably less water. 



XEROPHYTIC TYPES 



Alpine and subalpine meadows: light i; available water 12- 

 17% ; humidity 30-65% ; temperature 4O-65 ; 5O-75. 



ANTENNARIA SP. : diphotophyll 150^; epidermis i$ p.', cuticle 

 thin; chlorenchym (120 /A) i compact row prolate palisade cells 

 45 p.; compact globose sponge cells. (Plate IV, fig. 3.) 



Antennaria mucronata. 



Antennaria nardina: leaf 125 p.. 



Antennaria imbricata: epidermis 20 p., very wavy. 



Antennaria parvifolia: epidermis 20 p., wavy. 



DRYAS OCTOPETALA : diphotophyll 250 p. ; epidermis 20 p. ; cuticle 

 2 p.; chlorenchym (210 /*) 3-4 compact rows prolate palisade cells 

 35 p. ; loose irregular sponge cells. 



PSEUDOCYMOPTERUS MONTANUS PURPUREUS : diphotophyll 225 /* > 



epidermis 25^; cuticle thin; chlorenchym (i/5/u,) 2 compact rows 

 prolate palisade cells 50 p.; compact subglobose sponge cells. 

 (Plate IV, fig. 7.) 

 Fragaria glauca: sponge loose. 



