MORPHOLOGY OF REPRODUCTION IN GNETUM. 55 
Notes on the Morphology of certain Structures concerned in Reproduction 
in the Genus Gnetum. By Н. Н. W. Pearson, Sc.D., F.L.S., Henry 
Bolus Professor of Botany in the South African College *. — (Abstract.) 
[Read 4th June, 1914.] 
THE author records the occurrence of complete ovules with 3, and 
occasionally 4, envelopes on the lower nodes of spikes of Gnetum Gnemon 
bearing male flowers, and adds that true androgynous as well as pseudo- 
androgynous spikes occur in G. Gnemon, and probably in other species. 
Four types of spike are known, which constitute a sequence ranging from 
the strictly unisexual to the bisexual form. Wettstein’s opinion that 
evolution progressed from unisexual inflorescences towards a combined type 
is criticised, and the author favours Strasburger’s conclusion that the existing 
types are the result of reduction from a primitive hermaphrodite type. The 
morphology of the 4 envelopes present in some ovules is discussed : the 
middle of the normal 3 integuments is believed to be duplicated, the outer- 
most of the four being homologous with the outermost in the usual type. 
The presence of a bud subtended by the outermost envelope reveals a 
tendeney towards the development of axillary structures by which the spike 
of Gnetum might arise by proliferation from a primitive inflorescence (or 
flower) bearing a single terminal ovule. The presence of а bud in the axil 
of the outer member supports the view that ihe flower-envelope of the 
Gnetales has been formed by the specialisation of a barren leaf-structure. 
Certain stages, hitherto unrecorded, in the development of the male flower 
of Gnetum Gnemon are described : its antherophore is interpreted as foliar 
and as having been formed by the fusion of two filaments. 
The author proceeds to discuss the origin and morphology of the endo- 
sperm: he gives an account of our knowledge of the tissue within the 
megaspore in the different genera of the Gnetales, and describes the structure 
of the megaspore in Gnetum africanum. At an early stage there is a 
differentiation into a fertile micropylar region and a sterile chalazal region 
as in Welwitschia: the cytoplasm in the lower half of the megaspore is 
blocked out into compartments, and the septation presents many resemblances 
49 the condition described in Welwitschia. Bach compartment contains more 
than one nucleus, usually five or more. There is no septation in the micro- 
pylar region, The nuclei in each compartment in the chalazal region fuse 
as in Welwitschia, while the nucellar “ pavement tissue ” described by 
* Percy Sladen Memorial Expeditions in South-West Africa. (Assisted by Grants from 
the Royal Society.) 
