j 6 o Pearson.—On the Embryo of Welwitschia. 
This suggested the further possibility that the completion of intraseminal 
growth might be deferred until after the fall of the seed ; in certain species 
of Gnetum , as is well known, the embryo does not appear while the ovule is 
still in position, and this is probably characteristic for the genus. In the 
absence of any indications as to the later history of the terminal group of 
thirty-two cells it was provisionally compared with the corresponding region 
of the proembryo of Araucaria brasiliana , to which it bears a curious 
resemblance. 1 And although it was known that the ‘cap’ cells of Wel¬ 
witschia are not thrown off in the stages immediately following, 2 as is the 
case in Araucaria, it nevertheless seemed probable that the embryo was 
formed from similarly situated regions in the two cases, viz. from the 
so-called ‘embryonic plate’ (Text-fig. I, e.). It was further assumed that 
the cells of the lower ring in due course contributed additions to the 
suspensor. 3 
It was arranged that the Percy Sladen Memorial Expedition in South¬ 
west Africa should visit Welwitsch in Damaraland after the end of February 
in order to collect material of the later stages. The results now recorded 
have been obtained from ovules gathered there between March 2 and 9, 
1909. An expedition to Welwitsch’s own locality near Mossamedes in 
South Angola, in the following month, has yielded no additional information, 
as the older cones obtained there were diseased. 4 
This investigation has settled all the doubtful points referred to above. 
The development of the embryo, as far as the stage of Fig. 4, proceeds, 
apparently without any interruption, while the cone is still in position and 
intact; and since cones collected by Baines at Haikamchab on May 10, 
1861, contained ripe seeds, 5 it is probable that embryo-development is con¬ 
tinuous until the seed is mature. The period intervening between the 
occurrence of fertilization and the completion of the intraseminal growth of 
the embryo is thus less than four months. In this respect Welwitschia 
shows an agreement with Ephedra 6 rather than with Gnetum ; but in view 
of the extreme xerophytic conditions to which Welwitschia has become 
adapted this cannot be regarded as of phylogenetic significance. Stras- 
burger’s statement that the ‘ cap ’ cells are not thrown off is confirmed ; 
in the stage shown in Text-fig. 1 they are still the initial cells of the pro¬ 
embryo ; their descendants occupying a similar position retain this character 
until the superficial layer becomes dermatogen and a cell-mass underlying 
it at the apex is organized as a meristematic group ; the identification of the 
internal cell-plate (e.) as the ‘ embryonic plate ’ was therefore erroneous. 
The suggestion that the cells of the lower ring (x.) produce further additions 
to the suspensor is confirmed. 
1 Strasburger, 1879, Taf. xx. * 1. c ., p. 155. 
3 Cf. Hooker, 1863, PI* 10, Fig- 25. 4 Pearson, 1909 b. 
5 Hooker, 1863, P* 3 * 6 Land, 1907, p. 281. 
