Pearson.—On the Embryo of Welwitschia . 763 
mass. While the mechanical force developed by the whole system is 
without doubt of second-rate importance compared with the results of 
enzyme-action in front of the flattened, bluntly-pointed tip of the embryo, 
the crushed cells which commonly lie in contact with it bear witness to the 
exertion of a definite pushing force. 
No ovule in which the endosperm was not obviously withered has been 
found to be without an embryo. This tends to confirm the observation 
previously recorded 1 that the second phase of the growth of the trophophyte 
is dependent upon the occurrence of fertilization—either directly or through 
the embryonic activity which follows it. One case only has been seen 
in which the one remaining embryo in an ovule was clearly breaking down. 
The proportion of fertile seeds in normal cones appears to be fairly high, 2 
and the efficiency of seed-production in Damaraland is in striking contrast 
to the rarity of the occurrence of successful germination in that region. 3 
In early stages, as has been already recorded, 4 the ovule usually con¬ 
tains a number of proembryos ; but sooner or later all but one disintegrate. 
It very rarely happens that an advanced ovule is polyembryonic owing to 
the persistent development of more than one proembryo. In one such case 
the larger of two embryos (about the stage of Fig. 3) lies deep in the 
axis of the endosperm, while a second (younger than Fig. 1), having pene¬ 
trated almost to the depth of the former, has turned abruptly through 
an angle of 180° and now lies near the boundary of the disorganized region 
of the endosperm 5 with its apex directed towards the nucellus. This 
appears to be another instance of the readiness with which the Welwitschia 
embryo changes its direction of growth in response to a nutritive stimulus. 6 
While no case of the branching of the suspensor has been observed, poly- 
embryony due to the branching of the embryo itself is fairly common. 
This frequently occurs in the manner indicated in Fig, 6, in which an 
approximate bifurcation has taken place. Examples of lateral branching, in 
which an embryo produces a second one smaller than itself, are by no means 
rare (Fig. 7). While the former may be compared with the fission of the 
embryonic group in Pinas and other Conifers, the latter recalls the remarkable 
proliferation of the suspensor in Gnetum Gnemon , 7 in which there is little 
doubt that the outer cells of the massive suspensor are epibasal in origin 
as they are in Welzvitschia. More than two embryos in one ovule have 
not been certainly seen ; in one doubtful case there are perhaps three. 
That the polyembryony of Welwitschia is very much more limited than in 
Gnetum is in keeping with the higher degree of specialization to which 
1 Pearson, 1909, pp. 352, 370. 
2 Mr. Lynch informs me that of a considerable number of selected seeds sent to Cambridge from 
Damaraland in 1907, about 80 per cent, germinated. 
3 Pearson, 1907, p. 536. 4 Pearson, 1909 A, p. 368. 
5 Pearson, 1909 A, Text-fig. c. 6 h c., p. 364. 
7 Bower, 1882, p. 2S4. A similar proliferation occurs in G. scandens. 
