4o8 Boewig on the Histology and 



tributed, each consisting of from five to ten angular cells 

 with lignified walls. External to each protoxylem patch 

 and sometimes adjacent to it, or at other times separated by 

 what seems a fundamental tissue cell, is a patch of delicate, 

 thin-walled protoplasmic cells which feebly show wall mark- 

 ings in a few cells. 



Between each two of these bundles, about evenly dis- 

 tributed, are two bundles of phloem which have no corre- 

 sponding wood. These twelve phloem and four xylem 

 patches are quite constant. Figs. 5, 6 and 7 show the dis- 

 tribution of these into the roots. The wood patches break 

 up into smaller groups, and there seems a possibility of the 

 elements anastomosing before they run into the smaller 

 roots. The wood elements show chiefly spiral markings. 



The roots have no root cap. They bear copious hairs, 

 which are very turgid-looking, but quite short and mostly 

 club-shaped. These extend to the very tip of the root. 

 Sometimes the roots are ragged and broken off at the tip for 

 want of a root cap. They attain no great length, a seedling 

 nine inches long (Fig. 4, d) having roots half an inch long, 

 somewhat tenuous, pale, almost transparent-looking, and 

 very thin and feeble in appearance. The side roots are 

 much more vigorous usually than the tap root. The seed- 

 ling pictured had a larger tap root than is usual. In the 

 tap root, in fact, growth ceases early; it usually remains a 

 mere cone, and never has the appearance of a useful member. 



6. Histology of Mature Plant. ^ — A mature stem in cross 

 section shows externally a fairly well cutinized epidermis of 

 rather square cells, which have dense contents and contain 

 nuclei (8, i). Internal to this is a cortex (2) of four to six 

 irregular layers, with intercellular spaces and which is dense 

 with starch grains. The subepidermal layer is fairly regu- 



*Since my studies on this were completed, a paper has appeared 

 by A. T. Schmidt (in Oesterr Bot. Zeitschrift, V. 52, 1902), which 

 treats of the structure of the mature stem. 



