MODIFICATIONS OF FORM 199 



from one another to show that they are all cases of independent 

 adaptation, though the method of their perennation is essentially 

 the same in each. 



Such arrangements are biologically suited to life under strongly 

 marked seasons. The plant starts the active season of each year with a 

 sufficient store of nutrition already in hand to support rapid flowering. 

 In the remainder of the active season the store for the next year is 

 acquired by the expanded foliage leaves, and laid aside in the ripening 

 bulb. The bulb-dealer is understood to sell fully ripened bulbs : flower- 

 buds are already present in them, and only wait to expand. The pur- 

 chaser simply offers the conditionsfor active growth, and for the transfer 

 of the store to the flowering region. But to ensure a repetition of the 

 flowering in the next year he must fully ripen the bulb again as before. 

 This is often difficult, or impossible in the case of room-culture, or in 

 towns. Hence the dealer has a safe and continued market, based on the 

 ignorance, or the lack of opportunity of the public. The professional 

 bulb-grower secures normal perennation, with seasonal flowering ; the 

 purchaseris apt to forget that its continued success depends on nutrition 

 being maintained till the green leaves shrivel, and functional activity 

 ceases for the year. This dormant state, in which the bulb or corm is 

 bought, is itself an accommodation to seasonal drought. The bulb- 

 habit is widely spread, but it is specially characteristic of countries like 

 Southern Europe and the Cape, with a moist spring, but a dry and 

 hot summer. 



Symmetry, and its Modifications. 



The Root-System, developing in the soil, finds a medium in which 

 the conditions of temperature and moisture are relatively constant ; 

 but its form is liable to be strongly influenced by the texture of the 

 soil. Growing roots yield readily to the mechanical resistance thus 

 offered by any large obstacle. But if the roots develop in water, or 

 if the texture of the soil be fine and uniform, as it is in prepared garden 

 soil, the root-system develops with a regular symmetry. When, as 

 in Dicotyledons, there is a definite tap-root, this grows vertically 

 downwards, and the lateral roots radiate from it equally in all direc- 

 tions. Except for the effects of mechanical resistance, the root- 

 system of ordinary plants shows little departure from this regular 

 symmetry, while the individual root is typically cylindrical. It is 

 different where, as in epiphytes, the roots are aerial. Thus those 

 Orchids, which normally grow perched on the branches of trees, but are 

 cultivated in hanging baskets or on cork, often have roots of a flattened 



