764 Pearson.—On the Embryo of Welwitschia. 
the former has attained. There appears to be no record of the presence 
of more than one embryo in the mature seed of Welwitschia , and no 
doubt here, as in Gnetum Gnetnon, all but one sooner or later are crowded 
out of existence. 
The endosperm from which the stage shown in Fig. 3 was taken has 
almost exhausted the tissue in the remains of which it is enclosed. As 
Hooker 1 observed, most of this tissue is not part of the original nucellus, 
but is mainly formed by intercalary growth below the insertion of the 
integument. The endosperm is quite free from the surrounding tissue, and 
has a smooth firm surface composed of a well-defined and regular cell-layer. 
Its shape is little changed from that outlined in Fig. 89 k of my former paper. 2 
The upper third is, however, broader in proportion, and the lower region 
slopes more gently to the broad tip. The cavity marked c in the figure last 
cited has extended with the further penetration of the embryo. Between 
the embryo and the lower end of the endosperm the cells of an axial 
cylinder are looser than those nearer the periphery ; they contain for the 
most part very little visible starch and they are usually binucleate; 
occasionally they contain three or more nuclei. This condition is of 
common occurrence in the endosperm-cells of Gymnosperms in the neigh¬ 
bourhood of growing embryos and archegonia. 3 In Welwitschia the 
multinucleate state is the result of direct nuclear division. 
It is generally assumed that the seeds of Welwitschia retain their 
power of germinating for a long period. Some evidence bearing on this 
question is now forthcoming. A number of seeds collected in Damaraland 
in January, 1907, were stored in this laboratory. They were exposed to the 
atmosphere, but otherwise were kept as dry as possible. Four were sown 
in the last week of February, 1910. Of these, two have not germinated ; 
the cotyledons of one seedling appeared above the ground on April 4 
and those of a second followed after an interval of about fourteen days. The 
latter is living (May 31), but shows signs of damping off; the older of the 
two appears to be still thoroughly healthy and vigorous. These seeds were 
shed certainly not later than June or July, 1906. They have therefore 
retained their vitality for forty-three months, during which they have 
survived the almost continuously damp atmosphere of Cape Town and the 
low temperatures of three Cape winters—conditions which it might be 
expected would be particularly trying to the seeds of tropical desert plants. 
It is therefore probable that the most resistant seeds are capable of lying 
dormant for a much longer period under natural conditions. 
1 Hooker, 1863, p. 32. See also Pearson, 1906, p. 287. 
3 Pearson, 1 . c., p. 356. 
2 Pearson, 1909 A. 
