THE WHITE LILY 171 



Here, just as in Dicotyledons, the rootlet arises 

 from a deeply- seated layer of the parent -root, 

 namely, from its pericycle. The details of the 

 development are sufficiently shown by Figs. 68, 69, 

 and 70. The endodermis of the parent-root here 

 takes some part in the process, as it forms a sheath 

 around the developing rootlet during its growth 

 through the cortex. As this endodermal sheath serves 

 to absorb the cortical tissues, through which the 

 rootlet as it were eats its way, it bears the name of 

 the " digestive sac." When this function has been per- 

 formed, the sac is cast off, the whole permanent part of 

 the rootlet being thus formed from the pericycle. 



The origin of an adventitious root is similar to that 

 of a rootlet. Just as a rootlet arises endogenously 

 from the parent-root, so does an adventitious root 

 arise endogenously from the stem, and in both cases 

 it is the pericycle from which the new organ is 

 formed. 



SUMMARY OF MONOCOTYLEDONOUS ANATOMY 

 The general working of the vegetative organs in the 

 Monocotyledons goes on in the same way as in our 

 first type. In both, the green leaves, by means of 

 their palisade and spongy tissue, are the great organs 

 of assimilation and of transpiration. The leaves are 

 in communication with the stem through the vascular 

 bundles and the tissue immediately surrounding them. 

 The conducting tissues divide up their work as 

 follows : the wood serves chiefly to convey -the water 

 and mineral salts taken up by the roots ; the phloem 



