COLONISATION BY OTHER METHODS. 6"] 



valuable food material have to be preserved from the 

 attacks of animals of all kinds. Primitive man must 

 have been one of the most dangerous enemies of plants ; 

 and besides the attacks of man, plants suffered from 

 the depredations of boars, rats, mice, and other animals 

 that lived on the stored-up food, and against these it 

 was necessary to protect themselves. The rhizome of 

 the Male Fern is said to have been in severe winters the 

 chief article of food for the half-wild pigs in the New 

 Forest. Hence the wiry roots and dry, withered leaf 

 stalks which cover it as well as the remarkable secretion 

 (p. 274). The valuable food stores of the Potato, of Wake 

 Robin {Artim maculatuni), and of the Cassava {Manihot 

 utilissimus) are protected by bitter and even poisonous 

 secretions (from .012 per cent, to .042 per cent, of 

 prussic acid occurs in the bitter variety of the last 

 named), whilst the " Orris Root " of perfumery, which is 

 the rhizome of Iris florentina, and Ginger (also a rhizome) 

 have characteristic essences which probably are a little 

 too strong and highly flavoured for the tastes of their 

 enemies. The Anemone rhizomes^ on the other hand, 

 do not look in the least like anything edible, and 

 may thus escape notice. 



Plants with underground stores of food such as bulbs^ 

 conns, etc., are particularly abundant in hot dry climates 

 such as South Africa, from which country very many of 

 our most beautiful bulbous plants are obtained. In Great 

 Britain many of them are only conspicuous in spring ; 

 in late summer they have already finished their vegeta- 

 tion for the year and all their parts above ground have 

 withered away. This is generally quite necessary 

 because the grasses or the dense foliage of tall herb- 

 aceous species would certainly suffocate such compact, 

 short clumps as those of Ranunculus ficaria or the long, 



