On the Microsporangium and Microspore of Gnetum, 
with some Notes on the Structure of the Inflorescence . 1 
BY 
H. H. W. PEARSON, Sc.D., F.L.S., 
Harry Bolus Professor of Botany in the South African College . 
With Plates LX and LXI and six Figures in the Text. 
T HE study of the life-history of Gnetum has been attended by con- 
siderable difficulty; the results hitherto obtained are incomplete 
and not entirely harmonious. This is due mainly to the lack of adequate 
material for investigation. The localities in which most of the known 
species occur are not easy of access. The characters of the inflorescence 
are such as to preclude the possibility of obtaining a long series of stages 
at one gathering. In the female inflorescence in particular, the range of 
development defined by the youngest and the oldest flowers is a small one, 
and at any one time the flowers of all the inflorescences of a particular 
plant represent but a short series of stages. This is in striking contrast to 
the spike of W 'elwitschia, for example, in which, for a period measured by 
weeks, a large number of flowers developing in strictly acropetal succession 
furnish a crowded series ranging perhaps from the stage of the macrospore 
mother-cell to that of the advanced proembryo. In the female inflorescence 
of Gnetum a further difficulty arises from the fact that in many species 
( G . africanum , G. Buchholzianum , G. scandens , &c.), a large proportion of 
the ovules become arrested early in their history ; this may be due to an 
obvious disease, as in G. scandens , 2 or to more obscure causes, among which 
may perhaps be reckoned an insufficiency of available food. There are 
therefore good grounds for Lotsy’s conclusion that it is ‘ absolutely necessary 
to be a resident in the tropics if one wants to obtain a pretty complete 
series, and even then it is slow and difficult work ’. 3 Failing this we must 
resort to the less satisfactory process of piecing together the isolated facts 
established by various investigators working by different methods, at 
different times, on different species. 
1 Report of the Percy Sladen Memorial Expedition in South-West Africa, 1908-9, No. 15. 
This expedition was assisted by a grant from the Royal Society. 
2 Lotsy (’99), p. 4 7 ; (’03), p. 397. 3 Lotsy (’99), p. 47. 
[Annals of Botany, Vol. XXVI. No. CII, April, 1912.] 
