HOOKER LECTURE, 1917. 113 
of Paleontology are held as trustworthy, so far as they go. These are 
among the principles which may be observed in the quest of a Natural, 
that is essentially a Phyletie Classification. 
Those engaged in such enquiry will assent to the soundness of Pro- 
fessor Engler's Principles, which are indeed substantially those which were 
already in general use. But the feeling most prominent in the mind, after 
reading his statement of them, will be the hopelessness of the full realization 
of the quest under present conditions, in the case of Flowering Plants. The 
weakness of the evidence is specially marked in respect of the two lines 
which should be most prominent: viz. Anatomy, and the Palsontologica) 
record. Vascular Anatomy in Phanerogams has been robbed of its chief 
phyletie interest, as Dr. D. H. Scott has indieated, by the disappearance 
of the old centripetal wood, and the substitution of the new centrifugal 
wood, which is secondary botl in the individual and in the race. Only 
vestiges of the old wood remain in some few Gymnosperms. In the 
Angiosperms it is absent. Accordingly the study of vascular anatomy 
in them relates to relatively recent developments. The ancient structural 
documents have been irretrievably lost. 
Similarly, in the fossil record the documents are wanting for the phylesis 
of Flowering Plants. The outburst of the Angiosperms in the Mesozoic 
Period has left, so far as we yet know, little trace in the form of fossils with 
structure. Moreover, such impressions as are found relate commonly to 
leaves and stems, while flowers and fruits are wanting. The attention com- 
manded by the record of Cretovarium by Dr. Marie Stopes (Ann. of Bot. xxiv. 
p. 679) depended greatly on the rarity of the occurrence of such remains, 
for it harmonized readily enough with general anticipation. Three other 
circumstances affect the solution of the phyletie problem of the Angiosperms 
adversely. The first is the completeness of differentiation of the vegetative 
and propagative regions, whieh have diverged under adaptive modification 
each along its own line. The second is the directness of adaptation of their 
vegetative system to the environment, which obliterates the archaic, and 
tends rather to present the recent features. The third is the relatively dead 
level which these plants have reached in the details of their propagative 
process. The depressing uniformity of the pollen-sac and of the ovule 
in Angiosperms leaves little scope for comparative treatment in organs 
which might otherwise have been full of hope for the morphologist. : 
Before any general success can be expected in resolving the phylesis 
of Flowering Plants, so as to establish their main lines of descent, new 
evidence will be necessary. There will have to be an extension of the 
eriteria of comparison. Already there are signs of this in the more accurate 
comparison of details in the ovule, introduced by Van Tieghem. An 
intensified search will also have to be made after specimens showing 
