888 



JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



Cause of Direction of Branches. 



Branches of Trees and Bushes, On the Causes of the Direc- 

 tion of the. By J. Baranetzky (Flora, vol. Ixxxix. 1901, pp. 188-239 ; 20 

 cuts). — This is a careful study of the habit of trees, as caused by the 

 behaviour of their lateral branches, in which physiological and anatomical 

 data already known are enlarged by new researches, and notably by experi- 

 ments on weighting and supporting branches, and ascertaining the consequent 

 changes in the tissues developed. A most striking conclusion is that all 

 unilateral growth tends to determine an increased growth on the opposite 

 side. Thus any change of direction produced on the clinostat initiates a 

 series of reciprocating variations of intensity of growth on opposite sides 

 of the stem in the original plane of curvature ; as each cur\e is formed, 

 a counter-stimulus takes place, which finally masters the factor which 

 determined the curve, and consequently diminishes the curve. 



The open-air studies comprised the types (1) Bird Cherry, Ash, Maple, 

 Horse-chestnut, Euonymus and ' Syringa ' (PJiiladdphus coronarius) \ 

 (2) Lime and Elm ; besides, among Conifers, various Pines, especially the 

 Scotch Pine and the Fir (Picea excelsa). The weeping varieties of the 

 Ash, Elm, and Caragana arhorescens were investigated. For the results 

 the original paper must be consulted. A third section deals very fully 

 with the difference of length of the physiologically upper and under 

 side of shoots, and shows that this afiects the individual tissue elements. 



M.H. 



Cell Division. 



Cell Division {Beih. Bot. Cent. bd. xi. ht. 2, pp. 131 142, 1 plate).— 

 F. M. Andrews has investigated the karyokinesis in Magnolia and Lirio- 

 dcndron. The author sums up his results as follows : — 



I. In the First Mitosis. 



(1) The chromosomes arise from the resting nucleus as irregular 

 masses, without a previous formation of the usual and uniform spirem. 



(2) That the resulting chromosomes are mostly U-shaped, though 

 many are in the form of open or closed rings, or ellipses. 



(8) That they divide here again longitudinally. No longitudinal 

 division of the chromosomes was observed during the meta- or anaphase 

 of the first division. It probably does not occur, since the daughter 

 chromosomes of the first division lose their identity during the recon- 

 struction of the daughter nucleus, and, as these daughter nuclei pass into 

 the resting condition it is extremely difficult to conceive of the purpose 

 of a second longitudinal splitting of the chromatin during the first 

 mitosis. 



II. In the Second Mitosis. 



(1) The identity of the chromosomes, therefore, from the first to the 

 .second mitosis is not maintained. 



(2) That the chromosomes arise by the segmentation of an irregular 

 spirem, and are at first lumpy bodies. 



(8) That the chromosomes arise mostly in the form of shallow U's, 

 but in a few cases rings were formed. — G. F. S.-E. 



