FURTHER DEVELOPMENT OF WELWITSCHIA MIRABILIS, 583 
may be seen, in fig. vi11, how this happens. I have no evidence 
of “blind” endings of bundles in this part of the plant, though, 
owing to the great irregularity of course of the bundles, the proof 
of such endings would be very difficult. It cannot, therefore, be 
asserted that they do not exist (cf. ‘‘ Cycas,” De Bary, ‘ Vergl. 
Anat.,’ 630). 
In horizontal section the lobes of the crown present an appear- 
ance as in fig. 1x, a, B, the former being a section near the base, 
and the latter near the apex, of one of the lobes: Externally the 
lobe is covered with epidermis; beneath this is a tissue capable 
of division, in fact, this is the chief formative tissue of the lobe, 
by means of which it increases in bulk (cf. cmfra). Vascular 
bundles are scattered somewhat irregularly through the section, 
but they are evidently arranged with relation to the centre, the 
xylem being usually central. The peripheral bundles pursue a 
less regular course than those nearer the centre ; they anastomose, 
and run horizontally, &. These irregularities are again more 
marked in the later developed bundles, which are formed as the 
lobe increases in size. In large plants the course of the peri- 
pheral bundles of the crown is very sinuous, and difficult to 
follow (cf. zwfra). As before stated, the tissues at the apex of 
the lobe suffer a corky degradation, which starts at the apex and 
spreads backwards, including, as in the stock, not only paren- 
chymatous tissue and spicular cells, but also vascular bundles. 
We must now turn our attention to the région of greatest 
vegetative activity, viz. the base of the leaf groove. Ifa longitu- | 
dinal section be made through this, the whole mass of tissue is 
found to be in a state of active increase. The direction of the 
divisions is shown in fig. x, which represents under a higher power | 
the area marked off (x) in fig. vii, a, and includes part of the 
outer and inner lips of the leaf groove, together with the basal 
part of the plumular leaf. The divisions in the tissues, beneath 
the epidermis, which covers both lips of the groove, are most 
frequent in a direction parallel to the surface, so that the chief 
increase of bulk of tissue is in a direction perpendicular to the 
surface. ‘The divisions in the tissues of the stock below the base 
of the leaf groove are mainly transverse (as regards the axis of 
the stock). A growth in length of the stock is thus effected. 
The divisions at the base of the leaf itself are mostly in a similar 
direction, that is, at right angles to the surfaces of the leaf; 
an increase in length of the leaf structure is thus produced. The 
divisions in these several parts being constantly repeated in the 
same direction, the cells assume an arrangement in rows at right 
angles to the direction of division. Such rows may be traced 
distinctly throughout the greater part of the upper portion of 
plants of the stage of development of fig. 111, and this shows that 
