Galtiera bostonensis, gen. et sp. nov., a protostelic calamopityacean from the New Albany shale of Kentucky

Two parts of a single, anatomically preserved stem fragment form the basis of a new Lower Mississippian taxon that is characterized here in detail. Stelar morphology, leaf trace departure, secondary xylem, outer sparganum cortex, and Kalymma-like leaf bases provide evidence of taxonomic relationship with the Calamopityaceae. The primary vascular column is deeply three ribbed with protoxylem strands restricted to the periphery of the xylem. Trace departure is associated with a dextral shift in the position of primary xylem ribs such that the tip of each rib describes a helical course through the axis. The result is a Fibonacci phyllotactic fraction of at least 2/5. On the basis of our observations, we hypothesize that the protoxylem strands may comprise five sympodia and, further, that although protostelic in gross morphology, the primary vascular system of Galtiera might actually be more similar to typical eusteles of the Calamopityaceae than protosteles of any other major group. Sclerotic clusters and strands in the cortex are of interest because they are unusually numerous and are usually associated with the phloem either of the main stem vascular column or of leaf traces. The evidence is consistent with the hypothesis that this morphology reflects a pathological response by the plant to viral or other infectious agents.

Non-adaptive change in early land plant evolution

Primary vascular architecture of members of the Paleozoic Aneurophytales (Progymnosper-mopsida) is described. This architecture is somewhat more complex but fundamentally similar (homologous) to that of members of the Trimerophytina, putative ancestors of aneurophytes. It is suggested that the presence of complex stelar morphology in aneurophytes was epiphenomenal, a passive result of changes in growth and development in a trimerophyte-like ancestor. Specifically, I suggest that the evolutionary transformation in primary vascular architecture from haplostele to ribbed protostele was a direct consequence of changes that affected the vertical spacing and degree of organization of lateral appendages in early vascular plants. This view is in sharp contrast to adaptationist explanations of change in stelar morphology expressed by other authors and provides an example of non-adaptive change in evolution.

III.—Size in Relation to Internal Morphology. No. 2, The Vascular System of Selaginella

The influence of Size as a factor in the stelar morphology of the Filicales (2) and of some Primitive Plants (3) has already been discussed in the Proceedings of this Society. The aim of the present investigation is to determine by actual measurement to what extent Size may have acted as a causal factor in determining the structure and arrangement of the vascular system of Selaginella.

XXV.—Size in Relation to Internal Morphology. No. I.—Distribution of the Xylem in the Vascular System of Psilotum, Tmesipteris, and Lycopodium

In his Presidential Address to the Royal Society of Edinburgh in October 1920, Professor Bower (2) called attention to the question of Size in relation to stelar morphology, and advanced evidence (with particular reference to the Filicales) to show how the principle of similar structures has affected the internal morphology of the vascular system of plants. In dealing with the application of this principle he remarks that “the stems and roots of most plants are approximately cylindrical. The same is the case as a rule for their conducting tracts also. The cylinder is one of those solid forms in which the proportion of external surface to bulk is exceptionally low. Any deviation from the cylindrical form, either by external projections or by involutions, necessarily leads to an increase in the proportion of surface to bulk. The surface varies only as the square of the linear dimensions, but the bulk as the cube. It follows, therefore, that in carrying out any of those physiological functions of a living organism which depend on surface, as do all those of the acquisition and inter change of material, the actual size of the part which exercises that function is a matter of the greatest moment. The larger the plant is, the more dependent will it then be upon its form and detailed structure, not only for its stability, but also for the performance of its functions of absorption and transit of liquids and gases. This will apply not only to the external surface, but also to those internal surfaces which limit one tissue tract from another.” In illustration of this, examples were taken from the stems, tubers, and petioles of the Filicales, and the size-factor was also found applicable to the large prop-roots of palms, such as Areca and Verschaffeltia.