Bailey.] '^^ [May 1, 



parts more or less equally upon all sides, and the limit to growth is still 

 determined by the immediate environment of the given individual or of 

 its recent ancestors. Its evolution has been acephalic, diffuse, or head- 

 less, and the individual plant or tree has no proper concentration of parts. 

 For the most part, it is filled with unspecialized plasma, which, when 

 removed from the parent individual (as in cuttings and grafts), is able to 

 reproduce another like individual. The arrangements of leaves, branches, 

 the parts of the flower, and even of seeds in the fruit, are thus rotate or 

 circular, and in the highest type of plants the annual lateral increments 

 of growth are disposed in like fashion ; and it is significant to observe 

 that in the compositse, which is considered to be the latest and highest 

 general type of plant-form, the rotate or centrifugal arrangement is most 

 emphatically developed. The circular arrangement of parts is the typi- 

 cal one for higher plants, and any departure from this form is a speciali- 

 zation and demands explanation. 



Tiie point I wish to urge, therefore, is the nature of the obvious or ex- 

 ternal divergence of plant-like and animal-like lines of ascent. The 

 significance of the bilateral structure of animal-types is well understood, 

 but this significance has been drawn, so far as I know, from a compari- 

 son of bilateral or dimeric animals with rotate or polymeric animals. I 

 want to put a larger meaning into it, by making bilateralism the symbol 

 of the onward march of animal evolution and circumlateralism (if I may 

 invent tlie term) the symbol of plant evolution. The suggestion, however, 

 applies simply to the general arrangement of the parts or organs of the 

 plant body, and lias no relation whatever to functional attributes or pro- 

 cesses. It is a suggestion of analogues, not of horaologues. "We may, 

 therefore, contrast these two great lines of ascent, which, with so many 

 vicissitudes, have come up through the age?", as Dipleurogenesis and Cen- 

 trogenesis. 



The two divergent directions of the lines or phyla of evolution have 

 often been the subject of comment, but one of the sharpest contrasts 

 between the two was made in 1884 by Cope, when he proposed that the 

 vegetable kingdom has undergone a degenerate or retrogressive evolu- 

 tion. " The plants in general," he then wrote, "in the persons of their 

 protist ancestors, soon left a free-swimming life and became sessile. 

 Their lives thus became parasitic, more automatic, and, in one sense, 

 degenerate." The evolution of the plant creation is, therefore, held to 

 be a phenomenon of catagenesis or decadence. This, of course, is merely 

 a method of stating a comparison with the evolution of the animal line or 

 phylum, and is therefore of the greatest service. For myself, however, I 

 dislike the terms retrogressive, catagenetic, and the like, as applied to the 

 plant creation, because they imply intrinsic or actual degeneracy. True 

 retrogressive or degenerate evolution is the result of loss of attributes. 

 Cope holds that the chief proof of degeneracy in the plant world is the 

 loss of a free-swimming habit, but it is possible that the first life-plasma 

 was stationary ; at any rate, we do not know that it was motile. Degen- 



