raunkiaer's life forms 37 



due to the physiological dryness of the winter, while the deter- 

 mining factor in the Thymus formation is the actual dryness 

 of the summer. If we examine the species we can easily see that 

 the two formations belong naturally to two different climates, 

 for in the Thymus hiemalis formation many therophytes are 

 developed in a favorable spring. On the other hand it may be 

 remarked that within a single community we have such a limited 

 area that the explanation may not lie with climate alone. 



The Erica multiflora formation is by far richer in species than 

 the Calluna vulgaris, but in a biological sense does not differ 

 materiallj^ from it. The most widely separated from the heath 

 is the Arbutus unedo and Quercus coccijera, both of which are 

 much taller and possess larger leaves. 



In table 5, the formations are arranged according to their 

 height, the tallest at the bottom; it seems as if the decrease in 

 height is accompanied by a decrease in the leaf size. 



Here is shown a reliable basis for comparing and showing the 

 connection between closely related formations. It is especially 

 important in cases like that of the Mediterranean region w^here 

 the Maquis is the dominating type of formation, of wdde-spread 

 occurrence and exhibiting many variations in floristic composi- 

 tion. By means of the statistical method these variations may 

 be accurately determined and comparisons instituted regard- 

 ing each character and adaptation which can be, in some way or 

 another, expressed in terms of numerical value, as has been done 

 with reference to leaf-size. The same thing may be done \yith 

 reference to the protection of the stomatal openings, dimension 

 of stomatal openings, thick cuticle, hairiness and other ana- 

 tomical features. No difficulty, however great, must be allowed 

 to prevent the introduction, whenever possible, of exact quanti- 

 tative methods in plant geography. Thus only will it advance 

 beyond the vague and superficial descriptions of traveling plant 

 geographers. 



