MODIFICATIONS OF FORM 163 



temperature and drought than the growing plant. If then the 

 vegetative development, from germination to flowering and fruiting, 

 can all be completed within one growing season, an adverse period 

 can be safely passed as seed, and the species will survive. Practically 

 this has proved more effective in temperate than in tropical climates, 

 as is shown by the prevalence of annuals in the temperate Flora. On 

 the other hand, annuals are few in forest areas, which are less favour- 

 able to their growth than open ground. In particular the Arctic and 

 Alpine Floras consist almost entirely of perennials. This is easily 

 understood, since the vegetative season is there too short for the com- 

 pletion both of vegetation and propagation. The fact is illustrated 

 by the Alpine Flora of the Scottish Hills, which is distinctively Arctic 

 in its character. 



PERENNATION AND STORAGE. 



Perennation, that is the maintenance of the individual from year 

 to year, presents no difficulties where the seasons are equable, as in 

 many tropical areas, where perennials, growing steadily on from 

 year to year, form the chief element in the Flora. But in temperate 

 regions, with their strongly marked seasons, various adaptations of 

 the vegetative shoot besides that of leaf-fall may be seen, especially 

 in herbaceous plants, for tiding over the winter. They are mostly 

 associated with the storage of material, which is thus carried over 

 from one season to the next. The simplest case is that of biennial 

 plants, such as the Evening Primrose and Foxglove ; or, among culti- 

 vated plants, the Turnip, Carrot, Beet-root, or Onion. These in their 

 first year store their surplus nutriment in the vegetative organs at the 

 base of the plant, and use it up in flowering and fruiting in the following 

 year, after which the plant dies. Extreme cases of this method, 

 where the vegetative period may extend over several years, and is 

 terminated by flowering, fruiting, and death of the individual, are 

 seen in certain Bamboos, in Agave, and conspicuously in the large 

 Palm, Corypha. This plant, after years of vegetative growth, flowers 

 with an inflorescence thirty or forty feet in height, fruits profusely, 

 and dies. 



On the other hand, if the flowering be not profuse the perennation 

 may go on indefinitely, as in ordinary bulbs and herbaceous plants. 

 Each year a surplus of food-material is laid aside in underground 

 parts. In the autumn the aerial parts die away, but the stock remains 

 dormant and usually buried underground. Its store is thus protected 

 from the rigours of winter, till in spring fresh shoots develop similar 



