Reed.—On the Anatomy of some Tubers . 
543 
Anatomy of Tubers of Helianthus tuberosus. 
These tubers, like those of Solarium tuberosum , arise as swellings on 
underground stems, or stolons, which spring from the axils of scale leaves at 
the base of the main shoot. The stolon may at once swell up and become 
a tuber, or it may greatly elongate and give rise to a number of lateral 
tubers, finally terminating itself in a tuber. So far as these observations go 
this is different from what obtains in the potato, in that in the case of the 
latter the tubers do not arise laterally, as they may in H. tuberosus. 
Figs. 7 and 8, PI. XLII, show two young tubers. From these it will be 
seen that the tuber develops from the apex backwards. 
The anatomical structure of an untuberized stolon is that of a typical 
dicotyledonous stem. Fig. 9, PI. XLII, shows a portion of such a stolon, as 
seen in transverse section. It consists of a ring of a dozen or more vascular 
bundles, each of which is accompanied on the outer side of the phloem by 
a group of sclerenchymatous fibres (PI. XLII, Fig. 9, set.). Between the 
groups of xylem vessels there can be made out even at this stage small 
groups of xylem parenchyma (PI. XLII, Fig. 9, xy.p .). The pith and cortex 
are made up of parenchymatous elements of the usual type. 
As has been pointed out above, the transition from stolon to tuber 
is here very gradual, so that the manner in which the vascular elements are 
distributed in the tuber can be made out quite clearly. Tuberization is 
effected by two classes of tissue: (1) medulla, and (2) xylem parenchyma. 
Just at the region where stolon structure passes into that of the tuber, 
the cells of the pith commence to divide tangentially (PI. XLIII, Fig. 12 ,M.). 
These divisions commence around the periphery of the medulla, and 
gradually extend inwards until almost the whole of the pith is involved. 
The pith cells first enlarge considerably in a radial direction, and very 
soon tangential walls appear, and then the process is repeated again and 
again. As a result of these cell divisions in the medulla a very considerable 
amount of new parenchymatous tissue is added to the developing tuber. 
The cells resulting from the activity of this new meristem become arranged 
in definite radial rows (PI. XLIII, Fig. 13). 
For a time the parenchymatous cells of the medulla are the only cells 
which contribute to the formation of the tuber. 
After a time, however, divisions are seen to commence in the xylem 
parenchyma (PI. XLII, P'ig. 10, and PL XLIII, Fig. 12, xy.p.). These divisions 
aremainly tangential,and first make their appearance in those pockets of xylem 
parenchyma which are nearest the protoxylem side of the bundle (PI. XLII, 
Fig. 10). As a consequence of these tangential divisions the protoxylem 
becomes pushed towards the centre of the stem. A little later other pockets 
of xylem parenchyma become similarly meristematic, with the result that 
the whole xylem portion of the bundle becomes separated into small groups 
