Pearson .— On the Embryo of Welwitschia. 
761 
After the condition indicated in Text-fig. 3, the terminal initial cells 
(‘ cap ’ cells) undergo both periclinal and anticlinal divisions with the results 
that new cells are added beneath those of the plate and similar to them, 
and the number of cells in the superficial layer increases (PL LXIV, Figs. 1, 
6 , 7). The cells of the £ embryonic plate ’ (e.) may divide further ; they or their 
descendants lie at the extreme tip of the primary root-cap of which they 
form a part. Even as late as the stage of Fig. 3, all the superficial cells have 
not ceased to divide by periclinal walls, though many of them have no doubt 
become constituents of a dermatogen, and in somewhat more advanced 
stages they have all acquired this character. After the stage of Fig. 3, 
cell-division becomes localized in a more or less definite subapical 
growing region. The activity of this meristematic group results in the 
formation, on the side towards the suspensor, 
of a massive tissue whose cells are for the 
most part arranged in longitudinal rows. 
This is already indicated in Fig. 3, and 
becomes much more strongly marked in 
the axial core of later stages (‘ Periblem- 
saule ’)—see Figs. 4 and 5. For some time, 
therefore, the root-cap constitutes the greater 
part of the bulk of the embryo, in which 
character, as well as in the details of its 
formation, Welzvitschia remains true to the 
Gymnosperm type. In the embryo shown 
in Fig. 4 the original meristematic group 
has become divided into two by permanent 
tissue; separate growing points for stem 
(St.) and root (R) are thus established. The 
stem apex quickly becomes externally dis¬ 
tinguishable from the rest of the embryo by 
reason of its smaller diameter and dome-like 
surface (Fig. 4). Its elongation is very slow compared with that of the root ; 
in the embryo of the mature seed (Fig. 5), in which the two regions are still 
easily distinguished by the difference of breadth, the stem is hardly more 
than one-fifth of the length of the root. Strasburger showed that the 
cotyledons arise early from the stem-dome (Text-fig. 2) ; they grow fairly 
rapidly and usually somewhat unequally (Fig. 5). In the embryo of the 
mature seed, thin median sections disclose two small exogenous outgrowths 
from the stem apex, occupying axillary positions with respect to the 
cotyledons. Stages immediately following this are not available for com¬ 
parison, but there can be no doubt that these are the ‘ lateral cones L 1 
Their appearance thus early in acropetal succession to the cotyledons and 
1 Cf. Bower, 1881, pp. 579, 580, Fig. vii. 
Text-fig. 2. Outline of longi¬ 
tudinal section through distal end of the 
embryo of Welwitschia (after Stras¬ 
burger, 1879, Taf. xxii, Fig. 91). 
s. = stem-apex ; c. — cotyledons ; 
r. = growing-point of root. 
