STILT- OR BUTTRESS-ROOTS 



189 



which are disposed in a ring. The intervals between the mestome- 

 groups are occupied by relatively thin- walled bast-fibres, which add to 

 the mechanical strength of the fibro-vascular cylinder. A thick-walled 

 endodermis of the C-type (cf. Chap. VII., in. 1).) surrounds the stele. 

 The cortex consists of thick-walled parenchyma, which towards the 

 periphery passes gradually into a subepidermal zone of stereome of 

 varying width, composed of fibres witli very thick and abundantly 

 pitted walls. 



The mechanical system of the stilt-roots of Zea Mays thus consists 

 of two concentric hollow cylinders. The outer of these is entirely 



Fig. 66. 



Basal part of a stem of Zea Mays in L.S. V, V\. -Adventitious roots issuing from 

 a node above the level of the soil (0, 0\) which act as buttresses, besides assisting 

 the subterranean roots to fix the stem in the ground. For the sake of clearness only 

 a few of the rootlets are figured. 



made up of bast-fibres and is principally responsible for the inflexibility 

 of the organ : the inner includes the mestome elements and serves 

 chiefly to secure inextensibility. On the whole, however, the anatomy 

 of these stilt-roots seems to indicate that they are constructed as 

 inflexible rather than as inexteusible organs : otherwise it is not clear 

 why the solid fibro-vascular cylinder which is characteristic of the roots 

 of Grasses should here be dilated into a tubular structure. Stilt-roots 

 of this kind are not peculiar to the Indian Corn : very similar organs 

 recur in the genus Sorghum and in other tall and robust GRAMINEAE. 



The stilt-roots of Pandanus are adapted to their twofold 

 mechanical duty in quite a different manner. Here a transverse 

 section of the central cylinder reveals a large number of scattered 



