Gnetum africanum , with Notes on Gnetum scandens . 1125 
the inner integument proves them to be without doubt integumentary. 
Further, the complex nature of the outer integument in Gnetum makes the 
comparison there made between the seeds of the Gnetales, the Cycads, and 
some of the older types more striking, 1 and supports the attempt to 
refer them all to the same ground plan. The pollen chamber in Gnetum 
is clearly comparable with that described in the Cycads. 2 Other Cycadean 
features in the Gnetum inflorescence are the presence of the three 
concentric rings of bundles at the nodes, the middle one being inversely 
orientated to the others, and the occurrence of occasional concentric single 
bundles. 3 Similar features have been described in the ‘ peduncles ’ of 
Welwitscliia. The seed characters, however, of the recent Cycads suggest 
that any connexion between the two families is remote, probably only 
through common Pteridospermic ancestors. 
The seed characters in Gnetum also give most striking support to the 
other comparison drawn, in a former paper, between Welwitschia and the 
Bennettitales. 
VIII. Comparison between the Seeds of Gnetum and those 
of the Bennettitales. 
Conflicting and confusing as the accounts of the seeds of the Bennettitales 
at present necessarily are, the points of resemblance between them and 
Gnetum are even so most remarkable. 
(i) It will be well first to recall the detailed structure of the integu¬ 
ment m Bennettites Morierei. There is an outer layer which is expanded at 
the apex of the seed to form a palisaded tissue, which is considerably 
thickened (‘ assise rayonnante ’). 4 The inner layer of the integument is 
complex; next to the outer layer is a palisaded layer with thin walls 
(Lignier’s ‘assise plissee’), and internal to it are thin-walled cells which 
are brownish in colour (‘ tissu charnu ’) and a distinct fibrous layer. The 
fibrous layer, composed of elongated cells, extends downwards into the 
peduncle, and passes inside the vascular bundles, forming the pith of the 
upper portion of the peduncle ; in this region it is composed of much shorter 
cells with very thick walls. Bennettites Gibsonianus would appear to agree 
with B. Morierei , except that the expanded portion of the outer layer is there 
composed of oblong cells which are not so distinctly palisaded. 
Cycadeoidea Wielandii has a much thinner outer integument, also com- 
1 Coulter, 1908, p. 47, compares the seeds of Gnetum with those of Cycas and Ginkgo , since 
they all have a two-layered integument, the inner layer of which is stony, and both layers have 
a vascular supply. He regards the differentiation of the inner layer as a separate integument in 
Gnetum as a special development. I should regard it as a primitive feature, reminiscent of the 
Lagenostoma ground plan from which I believe all these seeds to have been derived. 
2 Lang, 1900. 3 Ante , pp. 1103, 1119 ; cf. concentric rings in the stems of Cycads. 
4 According to Lignier this outer layer is composed of ‘ tubular ’ cells, but Wieland refers the 
‘ assise tubuleuse ’ to the interseminal scales, and gives no special description of the outer layer in 
Bennettites except at the apex of the seed. 
