354 
Palaeontologie. 
the whole ränge of Palaeozoic seeds that have become known to us 
is the lack of an embryo. The petrifaction agrees in being at a stage 
which, in the light of recent Cycads, is to be interpreted as cor- 
responding to the time of fertilisation. The pollen-chamber is charged 
with pollen-grains, whilst in good examples the megaspore is filled 
with a prothallus which frequently shows indications of archegonia 
at its upper extremity. The normal fall of the seed may have fol- 
lowed pollination at a short interval, much as is reported for Cycas 
and Ginkgo to-day. The ‘resting period’ in these seeds would then 
perhaps coincide with the maturation of the sperms, whilst the sub- 
sequent embryonic history might have been carried through without 
a pause. The resting seed with an embryo marks a great advance 
on the Pteridosperm, an advance hardly less important to the wel- 
fare of the plant than was the earlier type of seed on the extended 
lifehistory of the filicinean prototype. 
The seed, as we find it in the majority of spermophytes with 
its resting embryo, shows definite adaptation to seasonal periodicity. 
It would be interesting to learn how far the seeds of plants long 
accustomed to uniform conditions, such as the rainy tropical forest, 
behave in this respect. Is there any solid foundation for the sup- 
posed ‘physiological dimorphism’ among seeds according to which, 
the earlier ripening seeds are adapted to an immediate germination, 
whilst the later ones are reserved for the following spring? 
The mention of the early germination of seeds brings to mind 
the most striking instance of all — that of the tropical Mangrove. 
Mr. Guppy has arrived at the conclueion that the Mangrove type 
of Vegetation is a very ancient one, dating back to the times when 
climate was more uniform and moist than we know it to-day. The 
viviparous habit he conjectures to have been once very general, 
whilst to-day this primitive condition is making its last stand along 
the tropical shores, and he supposes that the ordinary fruiting way 
of plants with caduceous fruits or seeds, that germinate after an in¬ 
terval, arose by a modification of the continuous viviparous method. 
But Sc hi mp er and others found no reason for regarding vivi- 
pary as other than an adaptation to special circumstances, an ex¬ 
treme condition that had arisen independently in several cycles of 
affinity. Moreover, if the viviparous habit were formerly of wide 
occurrence some traces of it might reasonably be expected in the 
fossil record. So far as can be ascertained, such have not been 
forthcoming, nor can I hear of any record of recent Mangroves 
being preserved in this way. Seeds and embryos appear to be so 
uniform on the whole that it is difficult to understand they could 
have passed through a viviparous phase in the later stages of their 
evolution. 
In glancing back at the early seed-structures one is Struck with 
the complexity of their Organisation as compared with the relative 
simplicity of modern seeds. The pollen-chamber, the large elaborate 
integument, and the complicated vascular arrangements, so cha- 
racteristic of the Pteridosperm seed, have for the most part passed 
away, giving place to much simpler structures. Occasional exceptions 
Magnolia , some Aroiäs, Sapotaceae, &c. show an unusual develop¬ 
ment of vascular tissue. Most astonishing of all perhaps is the inte- 
gumental tracheal sheath which closely invests the nucellus of Cas- 
sytha. This reduction in complexity may be accounted for on two 
grounds. In the first place fertilisation by motile sperms has been 
replaced by fertilisation by pollen-tubes. Instead of sperms being 
