48 
Paul Jaccard. 
For the corresponding zones of the Graian Alps the generic 
coefficient is 53% between 2600 and 3200 metres, 69% between 3200 
and 3500 metres. 
We therefore conclude, generally, that in the alpine zone the 
value of the generic coefficient increases with altitude, or, in other 
words, that with increasing altitude the number of genera decreases 
less rapidly than the number of species. 
This phenomenon, far from being the result of any specific 
influence of altitude, is in reality only a special case of the general 
law already stated relating the generic coefficient with the diversity 
of ecological conditions. It may in fact be established that in the 
degree that a station, such as alpine grassland for instance, becomes 
uniform, it becomes poor in species more rapidly than in genera. 
When the ecological uniformity is at its maximum the associated 
species almost all belong to different genera. But in the upper 
alpine zone, the increase of altitude, owing to its influence on the 
distribution of light, of heat, and of humidity, becomes a cause of 
ecological uniformity, and this is translated into terms of vegetation 
by the physiognomic uniformity of the vegetation of the heights. 
Only the species which have a close adaptation to such a habitat 
succeed in maintaining themselves. Among species of the same 
genus, only those persist which possess the most complete 
adaptation, to the exclusion of others, and so much so that most 
of the genera are represented only by a single species. 
Thus we are led to conclude that the genus is not a more or 
less arbitrary taxonomic unit, but a biological entity whose value 
appears in the distribution of plant species in a state of intensive 
competition. 
V. 
This conclusion applies equally, though in a less absolute 
fashion, to the great sub-divisions, classes or orders of plants. It 
proves true in every case for the great sub-divisions Dialypetalte 
and Gamopetalae, whose generic coefficients show parallel variations, 
and are usually almost identical with the generic coefficient of the 
whole flora. 
This appears in the following table:— 
Generic Coefficients of 
The area 
Jura meadow: 
Ormonts meadow 
W.T.D. 
12 localities, 
9 localities, 
661 species. 
240 species. 
92 species. 
Dialypetalae 
33% 
63% 
76% 
Gamopetalse 
33-6 
63 
74 
Total Flora 
33-4 
61 
79 
