122 ME. J. BALL ON THE DISTEIBUTION OF 



unworthy the pains which Mr. Ball hestowed upon it. It cannot fail to add a new 

 interest to the travels of botanists in this region. Each, of Mr. Ball's fifty districts will 

 afford a suggestive problem, if tested in the light of M. de Candolle's theory. 



The following extract from the lecture already quoted is important as showing the 

 principles which Mr. Ball adopted in framing his list of species : — 



*' It is not . . . easy to fix the limits of the Alps on the northern and southern sides 

 where the mountains gradually subside into the plains. On the south side especially 

 many plants whose natural home is in the low country have spread into the valleys, 

 and appear here and there as immigrants ; while, on the other hand, numerous natives 

 of the warmer slopes (many of them not known to grow elsewhere) do not ascend to the 

 higher zone, but cannot be excluded from the study of the Alpine flora. I have, as a 

 rule, omitted from my lists the plants of the plains that appear in the Alps only as 

 occasional stragglers, but I have included all the other indigenous species, although 

 some of them do not rise more than two or three thousand feet above the sea-level." 

 (Proc. B. Geogr. Soc. 1879, p. 566.) 



To this may be added a further passage giving the actual number of species which, 

 according to Mr. Ball's views, should be included in the flora of the Alps : — 



"I find in the whole region 2010 species, divided into 523 genera, included in 96 

 natural orders. But of these natural orders there are no less than 36 that are not at all 

 represented in the higher zone, and in the lower only by a few genera and species of 

 wide range. These 36 orders include 53 genera and 76 species — only an average of 

 about 2 species for each order — and evidently represent groups whose natural home 

 must be sought elsewhere. In addition to the 2010 species I reckon no less than 335 

 subspecies' — forms closely allied to recognized species, but distinguished by differences 

 more permanent and better marked than what are commonly called varieties. Most of 

 these, as well as a great many which I reckon as mere varieties, are counted as separate 

 species by many Trench and German botanists." (Proc. B. Geogr. Soc. 1879, pp. 567-S.) 



Mr. Ball had in many cases added to the names of the species a number of letters 

 the meaning of which for a long time baffied me. I am indebted to the acuteness 

 of Dr. Stapf for the discovery that they were intended to indicate the zones of altitude 

 at which the species occurred. As, however, Mr. Ball had left this feature of the 

 Table obviously incomplete, it is omitted. 



A less detailed statistical analysis of the whole flora in regard to altitudinal distribution 

 is, however, given in the lecture already cited. I quote the following : — 



" In ascending the Alps from the region of the olive, or the vine, to that of perpetual 

 snow, we find, as you well know, a continuous change in the aspect of the vegetation, 

 and botanists have distinguished various successive zones corresponding to these changes. 

 For our present purpose it will be enough to take account of three well-marked 

 divisions :— a low^er zone extending up to the limit of deciduous trees, an upper zone 

 including the higher pine forests and the Alpine pastures, and a glacial region where 

 patches of snow remain through the summer, and only a part of the surface is cleared for 

 two or three months, and even there sharp night-frosts frequently recur." (L. c. p. 567.) 



