ECOLOGY OF THE NAPLES FLORA. 159 



Smilax aspera, are highly characteristic of the woodlands and 

 thickets. Along the cliffsides occnr many plants with woolly or 

 silky pubescence, snch as Artemisia, MatfliioJa and JJeli- 

 chrysum. 



Some of the problems which suggested themselves in con- 

 nection with the vegetation forms of the Naples region were : 



I. The summer rate of transpiration of such sclerophyll 

 species as ilex, olive, lentisk and others. 



II. The functional importance of the summer deciduous 

 leaves of switch ]ilants, Spartium juiiceum and other legumi- 

 nous species. 



III. The manner in which the plants inhabiting cliffsides 

 almost waterless in sunnner support life through the dry months. 



IV. The longevity and relative activity at different ages of 

 some coriaceous evergreen leaves. 



Y. The relative activity of the sun leaves and shade leaves 

 of the same individual. 



The rate of transpiration of such highly coriaceous 

 leaves as those of the olive, the lentisk, and the ilex proved to be 

 very considerable.* At 21° O. and a relative humidity of 67 

 per cent, when supplied with plenty of water they transpired 

 from two-thirds to six-sevenths as much as ordinary mesophytes 

 like the comlnon pea and the European elm. The evergreen 

 buckthorn, Rliamnus Alaternus, transpired nearly twice as fast 

 as the elm. These facts indicate that the coriaceous character 

 of the evergreen leaves studied is partly to protect them from 

 injury during such emergencies as periods of excessive drought 

 and partly to withstand the severe whipping of violent winter 

 storms. 



The summer deciduous leaves of such switch plants as Spar- 



Hum are said, even by authors of the standing of Grisebach and 



Kerner, to be unimportant, having little to do with the gaseous 



exchanges of the plant. Xo attempt was made to investigate 



their photosynthetic w^ork; but it was found that on com])aring 



*Herman Ritter von Guttenberg obtained very high values in simi- 

 lar cases. See his Immergriine Laubblatt der Mediterranflora, Eng- 

 ler's Bot. Jahrb., 38, 4 and 5 Heft. 



