I INTRODUCTION 3 



regions of the tropics, also, there is a great preponder- 

 ance of perennial species, but with this difference, that 

 while in cold regions the persistent parts are under- 

 ground, in the form of woody stems, or bulbs, tubers, etc. 

 protected by the soil against extreme cold, in hot regions 

 they require no such protection, and are to a great 

 extent aerial. 



Uniform climates also appear to favour perennial 

 species. In the Sandwich Islands, for instance, species 

 of Violet and Geranium, of Composites and Caryo- 

 phyllacese, become shrubby. 



We owe to Messrs. Bonnier and Flahault a very 

 interesting memoir on the flora of Dauphine from this 

 point of view. They found — 



Auuual. Perenuial. 



In the region below the Pine forests . 60 per cent. 40 per cent. 



„ Pine and Grass region . 3.3 ,, 67 „ 



„ Upper Alpine „ . 6 » 94 „ 



As regards the character of the soil, etc., they give the 

 following table : — 



^Annual and 

 Biennial. 



Perennial. 



Stony and sand}' places 32 per cent. 68 per cent. 



Dry meadows . . 9'7 „ 90-3 „ 



Damp „ ... 13-8 „ 85-7 „ 



Woods and bushy places 4 „ 96 „ 



Aquatic . . 2-6 „ 97-4 „ 



Arable fields . . 88-8 „ 11-2 „ 



Many plants, as, for instance. Mignonette {Reseda 

 odorata), which are habitually annual, become biennial 

 if the flower-buds are pinched ofi'.^ 



The Flower 



If we examine a common flower, such, for instance, 

 as a Geranium (Fig. 1), we shall find that it consists of, 

 first, an outer envelope or calyx, sometimes tubular, 

 sometimes consisting of separate leaves called sepals ; 

 secondly, an inner envelope or corolla, which is gener- 

 ally more or less coloured, and which, like the calyx, is 



' Hildebrand, in Engler's Bot. Jahrh. ii. (1881). 



