AFTER A fascicled root system had been observed by Bryan (1936) in greenhouse plants of Cycas revoluta Thunb., an anatomical study of the fleshy adventitious roots was undertaken.2 Of principal interest is a centrifugally arranged primary xylem in addition to the regular centripetal metaxylem; this root, therefore, is mesarch. Among the few descriptions of Cycad roots, that of de Bary (1884) is the only one to mention reticulate tracheids, appearing as if secondarily in a centrifugal direction from the primary xylem plate. Material was obtained from plants grown in the botanical greenhouses of the University of Wisconsin. Each root after being washed was cut into segments approximately 1 cm. long; these segments were numbered consecutively, fixed with formol-alcohol-acetic or chrom-acetic solution in separate vials, and imbedded in paraffin. Several cross sections were cut from the proximal end of each segment; longitudinal sections were cut from the remainder of each segment that showed a distinct variance from those segments above or below. Staining was with safranin and fast green. One of the roots (A) most thoroughly studied was 17 cm. long; its segments were numbered A-i, A-2, .etc., progressing consecutively upward to A-19 at the stem end. Series B contained 2 much older and larger roots. Series D contained the 7 continuous segments of a 15 cm. root. Series E and F were from roots 4 and 6 cm. long, respectively. OBSERVATIONS. -The gross feature of the adventitious roots that is most conspicuous is their fleshy character. Root A has a maximum diameter of 15 mm. at a level about 1 cm. from the proximal end. In cross sections of thisroot at any level,, the cortex occupies almost 3/4 the total diameter of the root. Even the growing tip is blunt and massive. All the cortical cells arise in the meristematic region and become differentiated at once into parenchyma. It is chiefly the enlargement of each cell of the cortex to several times its original size that results in the growth in diameter of the whole root. The number of parenchymatous cells, counted in a radial direction, is almost exactly the same in a cross section near the tip and in one near the proximal end. At the proximal end of each root examined there are either 7 or 8 protoxylem points. By a merging from time to time of neighboring points, this number regularly decreases as the root is traced downward. In root A, the decrease segment by segment is as follows: A-19, septarch; A-18, hexarch; A-17, pentarch; A-15, tetrarch; A-13, triarch; A-8, diarch.