RELATION OF STRUCTURE TO FUNCTION IN ROOTS. 757 



on the branches; but they become detached, as described on p. 603, as soon as 

 they are from 30 to 50 cms. long, and falling with considerable velocity, bore 

 into the mud by their lower thickened end. It never happens that one of these 

 embryos grows down to the ground from the branch, and there is no doubt that 

 the long roots extending from the crown of the tree down to the mud originate 

 from the lower horizontal branches of the mangroves just like other columnar 

 roots. Columnar roots are distinguished from the flexible, cord-like, aerial roots 

 of aroids and other epiphytes (c/. p. 365) by their great resistance to bending and 

 by their possession of a characteristic mechanical tissue, in consequence of which 

 they have a totally diflerent internal sti'ucture, which, however, will be described 

 later on. 



Pei-haps the most imposing cases of development of columnar roots are exhibited 

 by the Indian banyans {Ficus nitida, Tsiela, and many others), which are usually 

 comprehended xinder the name Ficus Indica, one of which is illustrated in the 

 backgi-ound of fig. 185. To these also belongs the celebrated Asvhatta, the sacred 

 Fig-tree of the Hindoo (Ficus religiosa), beneath the shade of which Buddha is 

 said to have learned the vanity of existence and the mystery of the univeree. In 

 proportion as the boughs which project almost horizontally from the main trunk 

 of this tree become stronger, and give rise to branches and increase in weight, they 

 send out cylindrical roots which grow down to the ground, penetrate into the soil, 

 strengthen themselves by lateral roots, and serve as supports for the branches in 

 question. These columnar roots, which continue to grow in thickness, resemble 

 erect stems, develop leafy branches, and not only function as supports, but also 

 serve for the absorption and transmission of water and dissolved food-salts from 

 the ground. Below the crown of one of these banyan-trees we might imagine 

 ourselves in a. spacious hall of which the roof is supported on pillars; and since 

 the leafy covering of the crown is almost impervious to rain and sun, a weird 

 twilight always pervades these halls even during the daytime. Tradition states 

 that an army of 5000 men have encamped in the halls of a single banyan-tree. 

 Near the village of Dena Pitya, in Ceylon, there stands an Asvhatta under whose 

 shade a village of a hundi-ed huts is established, and in a single banyan-tree 350 

 large and 3000 smaller columnar aerial roots have been counted. When left en- 

 tirely to themselves the banyan-trees scarcely ever assume such gigantic pi'opor- 

 tions, because the ground under the crown is so dry and hard that the supporting 

 props which grow down often fail to penetrate it and are unable to take root 

 there; but in the trees held sacred by the Buddhists the rooting is assisted by 

 conducting the roots descending from the branches through long bamboo tubes, 

 and by breaking up and moistening the soil where they would penetrate into the 

 ground. 



The shape of roots differs materially according as to whether the plants to 

 which they belong are annual, biennial, or perennial. Annual plants produce as 

 many seeds as possible in the short period of vegetation allowed them, and provide 

 the embryos within the seeds, which have to travel about the world, with the 



