ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 67 



The organs treated of are spores of flowerless plants, seeds, fruits, pollen- 

 grains, &c. ; these are arranged in classes characterised by the nature of 

 the motion rather than by their morphological characters. 



Biology of Leaves. * — With immense wealth of detail, Prof. A. 

 Hansgirg treats of the great variety in the form and structure of leaves, 

 classifying them under a number of different heads. While in individual 

 cases the process is always obscure, yet, as a general law, the frequent 

 enormous difference in the form and structure of the leaves of closely 

 related species, and in other cases the minute resemblance between the 

 leaves of plants in no way related to one another, must be attributed to 

 natural selection acting through the internal laws of variation about 

 which so little is known. The archaic form of leaf from which all others 

 have been derived, was probably simple, entire, sessile, of delicate 

 structure, deciduous, glabrous, and without any special protection 

 against excessive transpiration, insolation, or cold. The highest type of 

 leaf is to be found in the higher Monocotyledons and Dicotyledons, 

 and in some ferns. The author classifies leaves in two great classes 

 from a biological point of view : — (A) Aquatic and Marsh leaves, Hydro- 

 phytes and Halophytes ; (B) Aerial land-leaves ; these are again classi- 

 fied under leaves belonging to Tropophytes, Mesophytes, Xerophytes, 

 Ombrophytes, and Halophytes. 



Phyllotaxis.f — Eejecting the various mathematical theories that 

 have been proposed to account for the phenomena of phyllotaxis, Dr. 

 A. H. Church has arrived at the conclusion that the whole subject is a 

 question of the mechanical distribution of energy within the substance 

 of the protoplasmic mass of the apex of the plant ; and that tho phenomena 

 of phyllotaxis are the result of inherent properties of protoplasm ; the 

 energy of life being in fact distributed according to the laws which govern 

 the distribution of energy in any other form. 



Stipules of Liriodendron.J — From the examination of a large number 

 of leaves of Liriodendron Tulijrifera, and a comparison with those of 

 some fossil species, E. W. Berry supports the view that the large 

 fugacious stipules of our living tulip-tree represent former leaf-lobes, 

 which, becoming separated, formed basilar lobes, then winged petioles, 

 and finally the modern stipules. 



Bulbils of Lysimachia terrestris.§ — Prof. D. T. MacDougal regards 

 the bulbils formed in the axils of the aerial stems of this plant as 

 representing a new category of propagative bodies. They are branches 

 of restricted development, and are formed under conditions unfavourable 

 for seed formation. They are free from transpiratory organs of any 

 kind, and resemble rhizomes in structure rather than the aerial stems on 

 which they are borne. The germination of the bulbil occurs without 

 any appreciable resting period, and is followed by the final stages in the 

 differentiation of the stele. The bulbil becomes the main axis of the 

 new plant, becoming converted into a rhizome. 



* SB. k. bohm. Ges. Wiss. Prag. Math.-nat,. CI., 1900, 142 pp. 

 + Ann. Bot., xv. (1901) pp. 481-90 (2 figs.). 

 % Bull. Torrey Bot. Club, xxviii. (1901) pp. 493-8 (2 pis.). 



§ Bull. N. York Bot. Card., ii. (1901) pp. 82-9. See Bot. Gaz., xxxiL (1901) p. 65. 



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