THE EOOT. 



19 



developed in the air, and subsequently descending, present themselves in 

 various conditions. One of the most remarkable is that which is observed 

 in the Mangroves (fig. 9) (Rhizophoraceae) , where the seed germinates 

 in the fruit while the latter is still attached to the tree, and drops down 

 its long radicle until it reaches the mud in which these trees grow, so 

 that the stem of the young plant is enabled to establish itself firmly in 

 the uncertain soil before it detaches itself from the parent. This is an 

 axial root. In the Banyan tree (Ficus indica) adventitious roots are fre- 

 quently developed on the branches, which, descending to the earth, pene- 



Fig. 10. 



Pandanus odoratissimus, the Screw-pine, with adventitious roots supporting the trunk. 



trate into it and become supporting columns, which ultimately assume 

 the appearance of trunks, and give the tree the appearance of a group or 

 even a grove of trees united together at their heads. The roots of the 

 arborescent Monocotyledons partake to a certain extent of the same cha- 

 racter; and those of Palm-trees are observed to arise successively one 

 above another in a spiral course near the base of the stem, growing out- 

 wards and downwards to penetrate the ground, the older ones ultimately 

 decaying. In the Screw-pines (Pandanvs. fig. 10) this is still more 

 striking and distinct, as the spiral line which they form is more open, 



