ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 215 



BOTANY. 



GENERAL, 



Including the Anatomy and Physiology of Seed Plants. 



Structure and Development. 

 Vegetative. 



Observations on Primary Leaves.* — Leon Dufour arrives at the 

 following conclusions. Certain species produce primary leaves of a 

 simpler form than the adult leaves, and as a rule the leaves pass by pro- 

 gressive stages from the simpler to the more complex form. Comparison 

 shows that the primary leaves of one species resemble the adult leaves of 

 an allied species. In other cases the primary leaves also are somewhat 

 complex, the degree of complexity varying in different species. Many 

 authorities hold that these simple forms have a genealogical signification, 

 and that a species with complex leaves will reproduce in its primary 

 leaves the form of the adult leaf of an ancestor. This is a striking illus- 

 tration of the law that the evolution of the individual (ontogeny) repro- 

 duces the evolution of the race (phylogeny). The author's investigations 

 confirm this opinion. It is reasonable to suppose that a species whose 

 leaves stop at a certain degree of complexity, is more nearly allied to an 

 ancestor with simple leaves than another which bears complex primary 

 leaves and still more complex adult ones. 



In the case of the Anemones studied, while it would be too much to 

 assume that A. palmata is descended directly from A. hortensis and the 

 latter from A. Pulsatilla, it is admissible that these species arise from a 

 common ancestor with simple leaves, and that they exhibit different 

 stages of evolution, culminating in A. Pulsatilla. 



Primary leaves possess, therefore, two striking peculiarities : (1) they 

 reproduce ancient forms ; (2) this reproduction is very faithful. The con- 

 ditions under which they are produced ensure them against modification 

 by external influences. The instances of Anemones and of Umbelliferte 

 bearing complex primary leaves do not disprove this theory. Individual 

 development can only reproduce that of the race by a contraction of time 

 and by the omission of certain stages — a phenomenon known as " meta- 

 genetic acceleration." 



Plants which from the outset bear complex leaves are then higher in 

 the evolutionary scale than those which bear simple primary leaves, and 

 in their more rapid development, certain stages known to their ancestors 

 are omitted. It is evident, therefore, that the study of primary leaves will 

 be of use in the discovery of the affinity of species. It suggests connect- 

 ing links that would not be suspected from observation limited to adult 

 plants. 



* Rev. Gen. Bot., xxii. (1910) pp. 369-84 (pis.). 



