618 Pearson . — On the Micro sporangium and Microspore of 
delicate (Fig. 17) ; an evanescent cell-plate is formed ; the two resulting 
nuclei lie quite free in the cytoplasm (Fig. 18). One of the two quickly 
divides again, the spindle being perhaps less indistinct than in the pre- 
ceding division. An evanescent cell-plate is formed in this case also 
(Fig. 19). After the completion of this division, the cytoplasm contains 
three free nuclei, of which two are usually a little larger than the third. 
They are most frequently arranged as shown in Fig. 20, but sometimes they 
lie in a row one above the other. This is the most advanced condition 
that has been found, and in anthers which are already protruding beyond 
the edge of the cupule all the pollen-grains are in this state. This is true 
also for G. Buchholzianum . There can be little doubt that these are adult 
pollen-grains, a conclusion which is in agreement with Karsten’s account. 
As is pointed out above, Karsten states that at the time of germination the 
pollen-grain contains only two free nuclei. One of the three must there- 
fore disappear ; presumably this is the one which does not participate in 
the second mitosis, and which is to be regarded as £ prothallial ’ in character 
and homologous with one of the three free nuclei in the mature pollen-grain 
of Welzvitsckia. 1 The other two nuclei are probably the one a tube nucleus, 
the second a generative nucleus. 2 No indication of the organization of 
a generative ‘ cell ’ has been observed. If such a cell is developed later, as 
is probable, 3 then in the germination of the microspore and the structure of 
the adult pollen-grain Gnetum differs in no important respect from 
W elwitschia. Between Gnetum and Ephedra , on the other hand, there 
is a wide gap. 
Summary. 
1. G. scandenS) G. africanum , and G. Buchholzianum have been in- 
vestigated. The study of the microsporangium and microspore has been 
mainly carried out on inflorescences of G. africanum. 
2. The male inflorescence is definite ; it bears a number of axillary 
rings of basipetally developed flowers. 
3. Other characters of the inflorescences are summarized on p. 6 14. 
4. The structure of the anther wall and the tapetum is similar to that 
described by Karsten. 
5. The pollen mother-cells are not free naked cells during the early 
stages of their development. But immediately before and after the condition 
of the nucleus known as synapsis, the cell-wall is extremely delicate and 
difficult to observe. 
6. Later the wall thickens irregularly and the mother-cells are not 
usually free from one another until the homotypic division is completed. 
7. The reduced number of chromosomes is probably twelve. 
1 Pearson (’06), PI. XVIII, Figs. 13-16. 
3 Karsten (’93) ; Lotsy, 1. c. 
2 Cf. Lotsy (’99), p. 94. 
