ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 481 



the pappus, in 113 genera of CompositaB, in which these points of struc- 

 ture vary in the same individual. This heterocarpy is most strongly 

 displayed in the genera Anthemis, Calendula, Hypochxris, Filago, aud 

 Buphthalmum. 



Theory of Phyllotaxis.* — Prof. S. Fchwendener replies at length to 

 Schumann's objections to his theory of phyllotaxis. He maintains that 

 the problem of the law of arrangement, e.g. of the flowers in the capi- 

 tule of a sunflower, cannot be determined by empirical observation, but 

 only by the application of geometrical and mechanical laws. 



Phyllotaxis of Impatiens g-landuligera.j — The varying arrange- 

 ment of the leaves in this plant can, according to M. P. Vuillemin, be 

 traced back to an original decussate type. The greater number of the 

 leaves on the stem are usually arranged in whorls of three, but, inter- 

 mediate between the lowest of these whorls and the cotyledons, is a 

 whorl of four, or less often two pairs of leaves arranged decussately. An 

 examination of the occurrence of buds in the axils of the leaves shows 

 that the whorls of three are false whorls, due to a torsion of the cotyledons 

 which origina'es within the seed. 



Roots and Mycorhiza of the Monotropacese. J — Prof. D. T. 

 MacDougal and Mr. P. E. Lloyd give the following as general charac- 

 teristics of all the Monotropacese at present studied. The roots lack 

 chlorophyll and usually also stomates. The stele is much reduced, and 

 consists only of perforated vessels and companion cells. The mycorhiza 

 encloses the tip and penetrates the epiderm, forming special structures 

 in the latter. The relation of fungus to host is one of pure symbiosis. 



j3. Physiology. 

 (1) Reproduction and Embryology. 



i Double Impregnation in Tulipa.§ — M. L. Guignard gives further 

 details of his observations on this subject. Talipa celsiana and sylvestris 

 are characterised by the slight differentiation of the cells developed in 

 the embryo-sac before impregnation. They are not, as in other plants, 

 arranged in two groups, one at the apex, the other at the base of the sac, 

 with the secondary nucleus towards its centre. Three of them only are 

 distinguished from the others by their morphological characters; two of 

 these, representing the nuclei of the synergids, occupy the summit of 

 the sac, and remain smaller, and in appearance more chromatic. The 

 third, situated towards the base of the sac, sometimes larger and some- 

 times smaller than the five others, grouped towards the centre of the sac, 

 exhibits at a very early period a differentiation from these latter in the 

 structure of its chromatic framework, formed of more delicate and mora, 

 condensed elements, accompanied by a large number of nuclei. The 

 central nuclei, on the contrary, exhibit distinct chromatic filaments, im- 

 bedded in which there are usually only one or two nuclei. The proto- 

 plasm of some of the nuclei is invested by a distinct membrane ; even 

 at the period when the pollen-tube passes its contents into the embryo- 



* S.B. k. Preuss. Akad. Wiss. Berlin, 1899, pp. 895-915 (5 figs.). 

 t Bull. Soc. Bot. France, xlvii. (1900) pp. 70-4. 

 J Bot. Gazette, xxix. (1900) p. 138. 



§ Ann. Sci. Nat. (Bot.), xi. (1900) pp. 365-87 (3 pis.). Of. this Journal, ante, 

 p. 349. 



