DEPARTMENT OF BOTANICAL RESEARCH. 65 



0.25 gram per gram fresh material. Thus the succulent form is 

 strikingly less acid than the normal type. 



In Castilleia latifolia two similar forms were also found even more 

 striking. As this was the subject of more extended experimentation 

 which will be reported elsewhere (see p. 85), only brief mention of it need 

 be made here. In general, after making allowance for the differ- 

 ence in leaf-form and so forth, the same morphological differences 

 were observed between the two forms as in the case of Ericameria. 

 The succulent type is much lighter in color, less hairy, though rather 

 more viscid than the typical form, and the thickness of the leaves is 

 about twice that of the normal. The acidity also is about half as 

 great in the succulent form, being 0.60 c.c. N/20 KOH per gram fresh 

 weight, while in the thin-leafed type it is 1.50 c.c. N/20 KOH for 

 the same weight. Obser\^ation of the distribution of the two forms 

 indicated that the difference in growth habit was referable to water- 

 supply. The cliff-edge, to which the succulent type is narrowly limited, 

 is dry; further back the water-supply of the host on which Castilleia 

 grows must be better. This was strikingly showTi by specimens of 

 thin-leaved type collected at the base of the cUff on the edge of the 

 sand, actually in closer contact with the so-called halophytic environ- 

 ment of the true beach plants, but in this case copiously irrigated by 

 the seepage at the base of the beach cliff. 



Two forms apparently referable to Erigeron glaucus were also found, 

 one on high cliffs overlooking the sea where the soil is very shallow, 

 the other the common type found everywhere near the sea-front. 

 The former was more succulent, the leaves measuring 0.60 mm. in 

 thickness, and in this case more hirsute than the typical form. The 

 thickness of the leaves in the latter case, which are merely finely puber- 

 ulent, M^as 0.45 mm. The acidity of the more succulent form was 

 0.75 c.c. N/20 KOH per gram fresh weight, while in the thinner- 

 leaved type the acid-content for the same fresh weight was 1.15 

 c.c. N/20 KOH. The difference in acidity is less striking here than 

 in the other two cases cited. 



In all these forms the succulent type is less acid than the normal 

 form. Of course, when the acidity is reduced to terms of dry weight 

 the relative acidities are more nearly equahzed, but even then there 

 is a disparity in favor of the less succulent tissue, which is more acid. 

 This circumstance, while not in accord with some of our usually 

 assumed characteristics of succulence, is of considerable interest. It 

 will be remembered that in investigations of succulents we commonly 

 do not have such strikingly different forms to compare. In cacti, 

 other things being equal, it is true that the more desiccated tissue is 

 the highest in acidity, but in these cases the comparative difference 

 in succulence is not so striking as in the cases cited. No doubt more 

 careful search would show other species of plants with such physio- 

 logical variations. 



