Palaeontologie. 
353 
hiscent to the indehiscent monosporal megasporangium finds its 
analogy in every group of plants. Where there is extreme numeri- 
cal reduction of the contained structures — be they spores or 
seeds — a multitude of cases in the Fungi, in the Algae, and the 
angiospermic flowering plants show that dehiscence tends to become 
obsolete. The failure to dehisce does not appear to be directly cor- 
related with any meehanical difficulty in ejaculation. 
We now come to the consideration of a most characteristic 
organ of the seed — the pollen-chamber. This cavity arises at the 
apex of the megasporangium, above the big megaspore, and is 
found in all the Palaeazoic seeds, with the sole exception, of the 
*seed-like’ structures in Lepidoccirpon and Miadesmia. The Utility ol 
the pollen-chamber is manifest, but its antecedents are quite un- 
known. Upon such a structure as this may have depended the suc- 
cess of the seed-method at a critical stage in its evolution. 
A great feature in the early seed types was the complexity of 
the integument. Protective envelopes are so commonly associated 
with reproductive organs, and the nutritive conditions are so favou- 
rable to their production, that a naked nucellus strikes one as ano¬ 
malous. If the Ferns which stand in possible relation to early seed- 
plants were ex-indusiate, like the Marattiaceae , recent and fossil, 
then no doubt the seed-coat is a new formation, having no true 
homology with, but merely homoplastic resemblance to, ordinary 
Fern-indusia. The only case of a naked nucellus that recalls itself 
is the rather mysterious instance of Lepidoccirpon in which is found 
the not infrequent occurrence of non-integumented megasporangia 
with the prothallus fully developed. 
The robust nature of the seed envelope, which was often dru- 
paceous, is in complete harmony with the whole character of the 
seed if the habit at its inception was a xerophilous adaptation; an 
improved method whereby the plant became independent of chance 
water at a very critical stage in the life-history. The relation be- 
tween the integument and sporangial body of recent Gymnosperm 
seeds is found to be an inconstant character, and the same is true of 
the fossils. In general character the relationship recalls that which 
obtains between the ovary and receptacle of an Angiosperm. 
The protective sheath, or testa, eventually appropriated other 
functions supplementary to that of protection, of which the most 
important must have been the reception of the pollen. A very strik- 
ing feature in all the Lagenostomas is the way in which the tip of 
the nucellus (where the orifice of the pollen-chamber is situated) 
projets beyond the integument. In these seeds the microspores had 
direct access to the pollen-chamber without first descending a micro- 
pylar canal. In the Medullosean seeds also the nucellus is distinguished 
by a long beak, but this beak does not extend to the surface, though 
it engages with the micropylar canal, and is continued some distance 
up. Though it can hardly be supposed that the long beak has been 
inherited from the ancestral sporangium, its presence may be none 
the less significant of what took place when the seed method was 
initiated. The direct pollination in Lagenostoma may well be a sur- 
vival from the old days when no proper micropyle existed. But when 
the micropyle closed in, the conservative nucellus would for a while 
endeavour to maintain direct communication with the exterior. The 
beak-like appendage on this view would be a new formation evolved 
pari passu with the integument. 
A peculiar and distinctive, though negative, feature common to 
Botan. Centralblatt. Band 107. 1908. 23 
