October 23, 1891. J 



SCIENCE. 



227 



ing from the base of the mid-rib, through the overgrown or 

 enlarged portion, to the extreme margin. This vein, later 

 on in the series, forms the mid-rib of the added leaflet. The 

 variation in the blackberry leaves emphasizes this interpreta- 

 tion. The trifoliate leaves seem to be struggling towards the 

 higher type represented by the five leaflets. This is seen so 

 plainly and so commonly that it is the exception when a 

 blackberry bush is found whose leaves do not illustrate vari- 

 ous transition stages of division. 



Potentilla Canadensis, common cinque-foil or five-finger, 

 furnishes an extremely interesting illustration of various 

 transition forms. It is an embryonic history of evolu- 

 tion in itself, which any one may read who observes it 

 closely. 



Examples might be multiplied ad libitum, for plants every- 

 where, both m cultivation and wild, repeat the same story 

 over and over again. 



The mode of division in pinnate leaves differs from that 

 just described in palmate leaves. In all pinnate leaves which 

 have been observed, with one exception, the newly formed 

 leafl.ets were given off from the terminal leaflet. The latter 

 will often be found unsymmetrical or lopsided, occasioned 

 by the extra fulness produced by this evolutionary tendency 

 towards division. The vein which is destined to become the 

 mid rib of the future leaflet becomes prominent, and the out- 

 line of the unborn leaflet, as it were, may be plainly seen ere 

 the division has proceeded beyond a slight notch. 



After a new leaflet has been given off, there seems to have 

 been a portion of the parent leaflet cut away; and if the new 

 leaflet be held close against this curved or cut portion, it will 

 be found that it corresponds with the outline of the new 

 leaflet. The opposite side of the parent leaflet will now be 

 found to be the larger, and the burden of adding the next 

 leaflet lies with it; after a leaflet has been given off from 

 each side the terminal leaflet may again become symmetrical 

 until a repetition of the process first described again takes 

 place. Tecoma radicans, Sambucus Canadensis, Ailanthus, 

 are familiar examples of this plan of division. 



The development of bi-pinnate and tripinnate from the 

 simple pinnate leaves was also observed frequently ; especially 

 was this noted in the leaves of Sambucus Canadensis. In 

 this case the new leaflets are given off from the oldest leaflet, 

 or that nearest the base, first on one side, then on the other, 

 preserving the symmetry with such precision that one is 

 awed by the beauty and harmony resulting from the work- 

 ings of vegetitive forces. 



As stated above, there proved to be one exception to the 

 general plan of division among pinnate leaves. This ex- 

 ception was found in the leaves of the rose. Search for 

 transition stages was made again and again in vain, when 

 one day, while examining the leaves, more from force of 

 habit than with the hope of finding anything bearing on the 

 subject of variation, the mystery was cleared away. 



At the base of the rose leaf two adnate stipules are found, 

 and these stipules themselves may be called the little mother- 

 leaves, for the leaflets of the rose appear to have been devel- 

 oped from the stipules. Specimens were found where the 

 "promise and potency" of the future leaf yet existed in the 

 stipules, awaiting, as it were, the magic touch of evolution. 

 The upper part of the stipule becomes enlarged and leaflike, 

 taking on more and more the shape and size of the normal 

 leaflet, until a perfect one is formed. A graduated and pro- 

 gressive series was frequently found, showing various stages 

 of transition, from the stipules alone to the mature leaf, con- 

 sisting of seven or more leaflets. The new leaflets may be 



readily discerned before they are given off or separated from 

 the stipules. 



The petiole lengthens as the leaflets are added, thus making 

 room for the newcomers. If a rose-leaf is examined, the 

 leaflets near the base will sometimes be found to be more or 

 less alternate, but becoming opposite in the direction of the 

 apex. This may be explained by the manner in which the 

 leaflets are developed, viz., alternately. 



The tendency in leaves to divide is manifested by many 

 simple leaves. Very often on plants bearing lobed leaves, 

 deeply lobed or cleft ones are found; and again, on those 

 plants where entire leaves obtain, more or less notched or 

 lobed ones often occur. 



An increased leaf-surface implies a larger amount of elabo- 

 rated plant food, and consequently an increased product, 

 either in rapidity of growth, beauty of bloom, quantity or 

 quality of fruit. Spencer says, '" Every change of form im- 

 plies change of structure; and with change of form and 

 structure comes change of function or quality." The same 

 laws of development are seen in the study of leaves as in the 

 social world. Heredity gives the direction in the bud or 

 germ, and the conditions or education unfolds it. If the 

 season is favorable, the leaf takes a pre-impressed direction 

 of growth, and surpasses its neighbors in assuming new 

 forms, and the average is passed ; while unfavorable condi- 

 tions may produce a degradation, or appeal only to the lower 

 stales of development. It will be understood, therefore, that 

 I do not mean to convey the idea that leaves undergo this 

 evolutionary divisi<.,n during a single season. On the con- 

 trary, the principles of "natural selection" and "the sur- 

 vival of the fittest" have left their impress upon the animal 

 and vegetable kingdom alike. Slowly but surely heredity 

 transmits the gain through good conditions to succeeding 

 generations. Through the long ages of the past this process 

 has been going on ; each generation has passed on the im- 

 provements it received from its ancestry, and has added its 

 own gain for the advance of its posterity. Each generation 

 comes forth with renewed powers to unfold in some special 

 direction, and I have endeavored to show, in a few cases, the 

 plan followed in the evolution of leaves. 



Mrs. W. a. Kelleeman. 



NOTES AND NEWS. 



The ninth congress of the American Ornithologists' Union 

 will convene in New York City on Tuesday, Nov. 17, 1891, at 11 

 A.M. The meetings will be held at the American Museum of 

 Natural History, Central Park (77th Street and 8th Avenue). The 

 presentation of ornithological papers will form a prominent fea- 

 ture of the meetings, and memhers are earnestly requested to con- 

 tribute, and to notify the secretary in advance as to the titles of 

 their communications, so that a programme for each day may be 

 prepared. 



— Mr. Michael E. Sadler, the secretary of the Oxford Univer- 

 sity Extension, has accepted the invitation of the American Soci- 

 ety for the Extension of University' Teaching to lecture under its 

 auspices in December and January of the coming winter. 



— Mr. Hal ford J. Mackinder, reader in geography to the Uni- 

 versity of Oxford, and staff lecturer to the Oxford University Ex- 

 tension, comes to Philadelphia next March to lecture under the 

 auspices of the American Society for the Extension of Univer- 

 sity Teaching, 1602 Chestnut Street, Philadelphia. 



— The American Society for the Extension of University Teach- 

 ing proposes to hold, during the holidays, a conference of the 

 leading college men of the country, to consider the subject of 

 university extension from a college point of view. This confer- 



