1000 i STOKEY— ANATOMY OF ISOETES 3"5 



up in the cortex than the old leaf traces. In fact it is not uncommon . 

 in sections of old stems cut at the very apex of the stem, to find in the 

 cortex a longitudinal section of a root making its way out. Hence, 

 although the stem and root regions are sharply marked off in the 



-. - m mm • . . 1 . • !•» 4- Vi rx PAftoV 



delimit 



are functional. 



fig 



fig 



<UC lUULllUIiai. Ill L11C JJIcUllS 311WVVH iii /*&"' *x? — » 



dead except a few at the bottom, and all the leaf traces except a 

 very few at the top. As the plant increases in size, the old leaf traces 

 are unable to keep up with the growth of the stem and are torn apart . 

 leaving the old stumps attached to the central axis, while the rest of 

 the leaf trace is carried out farther and farther by the growth of the 

 cortex, and in time is sloughed off. 

 The arrangement of the roots is described in great detail by Scott 

 '--•-- - urix, a three-lobed form. The two-lobed trunks 



Hy 



k ho\v no essential variation from 



-vn uu c^cnuai variation iiuni mat ^jy^t *** — 



necessary to give a detailed discussion of the subject. Fig. 6 illus- 

 trates the appearance of the lower part of the stem in cross-section, 

 showing the relative position of the roots of various ages. The roots 

 near the center, which are outlined by dots, are those in menstematic 

 condition; next to them are the mature active roots which are iro i- 

 cated by shaded circles; bevond the mature roots are those which are 

 dead and crushed. The relation of the sets of roots is indicated in 

 h 19 also. The arrangement of the roots in the two-lobed species 

 was first correctly worked out by Hofmeister; the youngest sets ^ 

 foots are those nearest the furrow ; and of those in the farrow , 

 ingest are at the ends. 



The structure of the roots has been described so many time s 

 * » unnecessary to take it up in detail. The most interesting featu 

 18 th at they are collateral and monarch, without showing any trac *s 

 of reduction. As the root bundle passes out from the vascular « s 

 ** a round or flattened bundle surrounded by parenchyma. 

 *<« distance from the stem, phloem replaces the parenchyma on 

 ** »*ay from the center of the stem. The phloem is always nrmtc 

 *° °ne side and is small in amount in comparison with the mi • 

 1 he re is also proportionallv much less than in the leaf trac s. 



THE ROOT 



At a 



the 



