PRESIDENTIAL ADDRESS. 729 



Lagenostoma may well be a survival 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 the whole 

 range of Palaeozoic seeds that have become known to us is the lack of an embryo. 

 Occasionally small-sized seeds are met with, as in Lagenostoma Lomaxi, and now 

 and then immature-looking stages, of which the best example is Renault's Cordaitean 

 ovule, so often figured in the books. But apart from such rarities the petrifactions 

 agree in being at a stage which, in the light of recent Oycads, is to be interpreted 

 as corresponding 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. All 

 these specimens will be dismissed by some as abortive, and any conclusions 

 drawn from the negative character as invalid. Without ignoring this contingency 

 another view is, of course, possible. The normal fall of the seed may have 

 followed 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 subsequent embryonic history might 

 have been carried through without a pause. This view gains .support from the 

 filicineaii relationship, for of course the fertilised egg of a Fern continues its 

 development without interruption. If the modification of the pteridophytic life- 

 history that culminated in these early seeds were directed, as seems probable, to 

 ensuring a greater certainty in bringing the gametes together under conditions 

 favourable to their union, it would follow that the other great Advantage 

 arising from the seed-habit was of later acquinition. In other words, the 

 ordinary seed with resting embryo 'was evolved by stages. There is a great 

 lacuna in our knowledge of the early adjustment of the embryo to intraseminal 

 existence. Whilst evidence of Palaeozoic seeds with resting embryos is altogether 

 wanting, we are confronted in the Mesozoic rocks with the Bennettiteae, all of 

 which possess a well-marked dicotyledonous embryo practically filling the seed- 

 cavity. It is mere conjecture to suggest that this change has been wrought in 

 response to some climatic stimulus, though the marked xerophilous facies of many 

 of the Mesozoic Oycadophyta seems quite consistent with such a view. Be that as 

 it may, one cannot foil to recognise that the resting seed with an embryo marks a 

 great advance on the Pteridosperm, an advance hardly less important to the 

 welfare of the plant than was the earlier type of seed on the extended life-history 

 of the filicinean prototype. 



This stage of the seed-history would be of exceptional interest if we could 

 hope to recover any morsels of direct evidence. As yet we remain in the dark as 

 to the morphological nature of the embryonic organs, how far we are dealing with 

 new structures produced from a protocorm, as Professor Bayley Balfour has 

 suggested ^ ; how far they represent the old filicinean organs adjusted to intra- 

 seminal life. Whrtt chance there may be of the solution of this difficult problem 

 by the application of other methods may emerge perhaps from the discussion on the 

 phylogenetic value of early seedling characters which is to be opened next Tuesday 

 morning by my colleagues Mr. Tansley and Miss Thomas. 



Reference has already been made to the view that 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. The point does not appear to have been very fully reported on. 

 Indeed there is a rich field for both observational and experimental work upon 

 obscure seed-problems awaiting any one who can devote continuous attention to 

 the subject. Is there any solid foundation for the supposed 'physiological 

 dimorphism ' among seeds according to which, as one reads in the older books, the 



' Presidential Address, Section K, Glasgow, 1901, p. 9. 



