338 AMERICAN MIDLAND NATURALIST 



epidermis of the stem. As a rule even in the older roots there is 

 but one series of intercellular spaces more or less oblong and 

 irregular in the cortex and with their ends pointing to the outside 

 and inwards to the stele or anticlinaly while in the stems they are 

 periclinal (Fig. la). Only one series of the larger spaces are found 

 in the root and several in the stem, though in the former a few 

 smaller ones are occasionally met with (Fig. ib). Only one to three 

 layers of cells are found between the larger spaces and the stele 

 inclusive of the endodermis. The cortex of the larger adventitious 

 roots (which were the only ones found for study) has a large 

 number of chlorophyll grains even as far inwards as the endodermis 

 excluded. Nor is chlorophyll found in either the epiblema or the 

 palisaded hypodermal layer of the older roots (Fig. 2). The stele 

 has a wood bundle of the radial type and the xylem is exarch 

 pentarch, the phloem alternating with the xylem rays. Just 

 outside of each phloem strand is a latex tube containing a brownish 

 somewhat resinous substance. The tube is surrounded in this 

 case by four secreting cells in the older roots (Fig. 3) though in 

 young specimens these are not as yet well differentiated or developed 

 These latex tubes are rather straight mostly unbranched tubes 

 with four secretion cells around them (Fig. 3) and are found 

 throughout the plant, and in the stem the secretion cells are 

 more than four, usually about six. (Figs. 5, 8, 9, 13, 17). The peri- 

 cycle is rather well differentiated as a marked layer of medium 

 sized cells in young parts of the roots, but later it loses to some 

 extent its characteristic appearance the cells of the cortex seeming 

 to pass by gradual variations of size to those of the stele. Ver}- 

 little secondary change takes place in the stele especial in the 

 xylem (hadrome) portion thereof; the ducts always are few in 

 number as would be expected in this case because of the needless- 

 ness of these water conducting vessels in aquatic plants. The 

 larger vessels formed later as metaxylem or perhaps secondary 

 xylem are scalariform pitted, those of the protoxylem are annular 

 and later spiral transitional to pitted. Longitudinal section of 

 the root shows the peculiar variations of the tissues in the root 

 in a marked way (Fig. 4). From the exterior we have in order 

 the outer layer of cells (a) and the hypodermal layer (b) these 

 two both devoid of chlorophyll. The cortical cells on both sides 

 of the large intercellular spaces resemble one another, and bear 

 chlorophyll in larger or smaller quantity depending on the exposure 



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