814 



THE AMERICAN NATURALIST 



[Vol. XLl 



characters adapted to drought in environments in which they are 

 unnecessary is that the present day phints liave inherited these features 

 from ancestral forms which grew under xerophytic conditions.^ Miss 

 Stopes, however, argues that in the conifers the xerophjiic character 

 is not to be regarded as an inlierited adaptation but as correlated with 

 the peculiarities of the conducting system of the stem. The gymno- 

 sperms have a much more primitive wood structure than the angio- 

 sperms and a much lower capacity for the conduction of water. It is 

 this lower efficiency as conductors of water that necessitates the xero- 

 phytic character of the foliage, — not the environment. In other 

 words, the author regards the xerophily of tliis grouj) as pliylogenetic, 

 not adaptive. 



^Yith Miss Stope's general conclusion tliat tiie xeropliily of the 

 Coniferales is phylogenetic and not ecological, Moss agrees (New 

 Pliytologist 6 : 183-185. 1906),2 but he feels tliat there is an untenable 

 assumption running through the wliole of her argument. This 

 assumption is that the conifers in question are more pronounced 

 xeropliytes than the angiosperms witli which tliey are ecologically 

 associated. The xerophily of the gymnosperms is seen in tlie greatly 

 reduced surface of the acicular leaf, whereas that of the angiosperms 

 takes the form of a deciduous habit by which the transpiration is 

 reduced to practically zero during tlie season of physiological dryness 

 of the soil. He finds that in many instances deciduous angiospermous 

 trees which are commonly regarded as mesopliytes, extend into liigher 

 altitudes and latitudes tlian conifers which are generally (biassed as fine 

 examples of xerophytes. Furthennorc, h<' finds that among both 

 conifers and dicotyledons, the (hM iduous siMcii-s arc tlie ones which 

 extend the farthest^ nortii. 



In view of these facts Moss would consider that the xerophily of the 



' Clements (Res. Meth. Ecol. 127, 1905) has suggested that the xerophytic 

 characters of bog plants are not due to the "physiological dryness" of their 

 substratum as proposed V)y Schimper and generally accepted, but to the 



phytic cnx iroiiniciits ir«^ would therefore suggest the origin of stable adap- 

 tive struct tiKv- wliich p(Mr-ist when the forms which had acquired them are 



Coniferal. i-^ inherited and not acquired, I do not proiio-<^ to d<'al. a-^ Mi-'s 

 "inherits 1 " he e\idently means phylogenetic in the set ' ■ 



