the ancestors of the coniferous stock, namely the Cordaitales. Taking first the very important criterion from the standpoint of the systematic arrangement of the Coniferales, the organization of the female cone, we find little to justify the recent contention of Professor Seward and his students and of Mr. Thomson, that the ovulate cone of the Araucarian conifers is of a different morphological order from that characteristic of the remaining coniferous tribes. It is perfectly clear that not only in the more primitive species of the living genus Araucaria but also in the cones of the Mesozoic representatives of the Araucariineae, described by the present writer either independently or in collaboration with Dr. Arthur Hollick, that the Araucarian female cone, like that of the other tribes of conifers was originally composed of cone-scales with a double system of bundles, independently emanating from the cone axis and of inverse orientation. Consequently whatever explanation is adopted for the double system of bundles in one case must be adopted in all. Attempts to read the Araucariineae out of the conifers must continue so long as the view is adhered to that they represented the primitive elaboration of the coniferous stock. It is a noteworthy fact that Professors Penhallow and Seward as well as Mr. Thomson, who much as they disagree in other matters, are in harmony in regarding the Araucariineae as distinct from other coniferous tribes and at the same time as the primitive representatives of the stock. 51 The recent investgations of Mr. A. J. Eames appear to make it perfectly clear that whatever explanation is adopted of the organization of the female strobilus in the Araucariineae, must hold likewise for all the remaining tribes of Conifers.

If we turn our attention now to the gametophytes, we arrive at similar conclusions, if our logical processes are based on the established principles of biological science. Taking first the male gametophyte, we find a method of germination of the microspore unlike that found in any other gymnospermous group, which has been inaptly denominated by Mr. Thomson as 'protosiphonogamic.' Certainly we would not expect to find the primitive type of pollen tube formation in a group in which the pollen no longer reaches the apex of the ovule, as it characteristically does in all other known groups of Gymnosperms, living and extinct. The peculiar germination of the pollen of Agathis and Araucaria, on the cone scale and not on the apex of the young seed is an unmistakable stigma of aberration. The contents of the pollen tube likewise vouch for the highly specialized con

51 Ann. Bot. Ined.

dition of the Araucariineae. Here the two prothallial cells common to the Abietineae and the equally ancient Ginkgoales become proliferated into a large number, doubtless in correlation with the extreme length and meandering course of the fertilizing tube. Moreover the absence of a stalk cell in connection with the setting off of the body cell, which gives rise to the two sperm cells, is a clear and outstanding feature of aberrancy. Mr. Eames in the memoir, already cited, has shown moreover, that in the organization of the female gametophyte, the structure of the archegonium, the nature and functions of the archegonium neck, as well as in the method of penetration of the pollen tube and the development of the embryo, the Araucarian conifers manifest not a primitive but an extremely aberrant condition. They are in fact comparable to a large degree in their systematic position with the edentate fauna, likewise characteristic of the antarctic region, Developmental investigations on the zoological side have recently shown that the edentulous features which have been until the present time regarded as a primitive feature of this group are in reality marks of aberrancy, since a more abundant dentition, at first makes its appearance in the embryo.

Reviewing all the evidence in the light of many recent investigations both in general morphology and in the morphology of the conifers in particular, it is clear that it is the anatomical features of the reproductive and vegetative organs, which give us the most reliable criteria as to the evolution of the coniferous stock and above all in the present connection, as to the evolution of the Araucarian tribe. The anatomical conditions in the living forms cannot be understood without careful comparison with the organization of those which are now extinct. Basing our conclusions on these criteria, the result is reached that the Araucarioxylon type has been derived from the Pityoxylon type and as a consequence formerly possessed the opposite pitting, the bars of Sanio, the strongly pitted rays and the resin canals of the ancient Abietineous woods. Some of these characters are still to be observed in primitive regions of the existing Araucariineae, while others are to be inferred from a consideration of the organization of Araucarian forms now extinct. It is further clear that the external form of the reproductive structures and the organization of the gametophytes supplies as little light, regarded independently from the anatomical organization of the reproductive and vegetative parts, for the interpretation of the true course of evolution and affinities of the ancient but highly aberrant coniferous tribe, the Araucariineae as is the case with the corresponding structures in the Bennettitean

tribe among the Cycadophyta. It is finally clear that morphologists will find it necessary in the future more and more to adopt certain general working principles, as in the case for example in the sister sciences of chemistry and physics. If there prove on trial to be no generally applicable fundamental principles in morphology, that branch of biological science cannot be too soon cast into the outer darkness, which prevails outside the scientific view of nature.

1.

GENERAL CONCLUSIONS.

The Araucariineae cannot have been derived from the Cordaitales since they possessed primitively a number of features which so far as our knowledge goes, never existed in the Cordaitean stock.

2. The Araucarioxylon type is derived from ancestral forms, ⚫ which possessed opposite pitting, bars of Sanio, strongly pitted rays and horizontal and vertical resin canals.

3. The primitive existence of these features in the ancestral type from which Araucarioxylon has been derived, show clearly that it has taken its origin from the Abietineous Pityoxylon type.

4. This conclusion is entirely confirmed by a consideration of the reproductive structures both sporophytic and gametophytic.

5. Any hypothesis as to the origin of the Coniferales in general must start with the Abietineae as the most primitive tribe.

6. It is absolutely essential to the progress of plant morphology, that investigation be carried on in connection with the elucidation of the general working principles of the biological sciences.

7. The comparative, developmental, paleobotanical and experimental investigation of the Coniferales is likely to throw more light on the stable and sound general principles of biology, than that of any other large group of animals or plants, on account of their great geological age and remarkably continuous and complete display, both as regards external form and internal structure in the strata of the earth.

BOTANICAL LABORATORIES OF HARVARD UNIVERSITY,

17th, June, 1912.