4o8 BOTANICAL GAZETTE [may 



with minute roots attached to the older tapering roots of Artemisia 

 pycnocephala, in a manner indicating that the dependent nutritive 

 relation is not an important one. That the appearance of suc- 

 culence in this plant has no connection with its parasitism is 

 supported by the fact that a similar state was found in Erigeron 

 glaucus and Ericameria ericoides which are found in the locality 

 near Castilleja. 



Measurements of the thickness of the leaves of the two types 

 show that the thin leaf averages about o .5 mm., while the succulent 

 one ranges from i to i . 5 mm. Examination of sections shows that 

 the structure of the leaves is mainly differentiated by the size of 

 the cells. While nearly dorsiventral in position when young, 

 structurally the leaves appear almost bifacial, with 2 or 3 rows of 

 vertically elongated cells on each face. In the thin-leaved type 

 these cells are about 35X25 ju- while similar cells of the succulent 

 leaf are 110X30 /x. Thus the increased thickness of the leaf is 

 due chiefly to the enlargement of the cells vertical to the flat surface 

 of the leaf. 



There is naturally a disparity in the relation of fresh to dry 

 weight in the 2 forms. Averages of a number of determinations 

 show the following figures: mesophytic t^^^e, i gm. fresh young 

 leaves, o. 193 dry weight; succulent type, i gm. fresh young leaves, 

 o . 1 13 dry weight. In general the succulent type yields only three- 

 fifths dry substance per unit fresh substance compared with the 

 other form. 



The acidity relations are also different. The succulent leaves 

 are much less acid than the thinner ones. In table I averages of 10 

 or more determinations indicate the difference in acid extracted, 

 and also the amount of water absorbed after 24 hours' immersion. 

 As might be expected, the acidity relation of the 2 forms approxi- 

 mates more closely when reckoned according to dry weight than 

 on the basis of fresh weight. Even then, however, the young 

 active leaves show a considerably greater acidity in the thin type, 

 a notable departure from our preconceived conceptions of acidity 

 in relation to succulence. It may be said, however, that direct 

 comparisons of acidity of a plant of the same species in a mesophytic 

 and succulent condition do not seem to have been made. 



