iqiq] DORETY—DIOON 255 



Seedling 



The primary root persists indefinitely as a tap root. Large 

 quantities of starch are transferred to it through the cotyledons, 

 and it becomes large and swollen. The small lateral roots arise 

 in whorls, usually of 4, and become a matted mass of fibers. Almost 

 all the greenhouse grown seedlings have their roots hyper trophied, 

 and the root tips have the characteristic tubercles described by 

 LiFE^ in Cycas. 



The first leaves are yellowish scales, although thick and fleshy. 

 They bear stipules like those of the foliage leaves, and some of 

 them manifest the typical circinate venation (figs. 10, 11), The 

 true leaves have been described by Chamberlain in the work pre- 

 viously cited. The first true leaves of several of my seedlings had 

 as few as 6 pairs of leaflets (fig. 9), but most of them had 12 or 

 more. There is great variation in the size of leaves of plants grown 

 in the same conditions and from the same sized seeds. One plant 

 bore small leaves with leaflets 2x0.3 cm., while another just 

 beside it bore on its first leaf 12 pairs of leaflets, each one of them 

 6X1.1 cm. Imitation of the moist air conditions under which the 

 first leaves of Ceratozamia became foliage leaves was unsuccessful 

 with Dioon spinulosum. 



The stele of the primary root is tetrarch, changing to diarch in 

 its later formed portions and in the lateral branches. The relative 

 size of the vascular cylinder to the whole root in various levels is 

 shown by figs. 16-19. I^ the hypocotyl the diameter of the vascu- 

 lar cylinder is only about one-seventh that of the whole axis. The 

 manner in which the radial position is achieved in the root is illus- 

 trated in figs. 18 and 19. 



The leaf traces are always endarch and collateral, and their 

 arrangement in the petiole as shown in cross-section presents the 

 well known omega-shape. Branching and anastomosis are frequent 

 throughout the petiole, but there is in general a diminution of 

 traces toward the top of the leaf. 



The plant is a much more rapid grower than Dioon edule, and 

 is far more graceful. Under favorable conditions in the greenhouse, 



' Life, A. C, The tuber-like rootlets of Cycas revoluia. BoT. Gaz. 31:265-271. 

 1901. 



