ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 555 



Growth of Root-tip.* — H. Lundegiirdk rinds that there is a certain 

 definite relation between the condition of nuclear division and the 

 rapidity of growth of the cell. The increase in volume of the nucleus 

 which takes place during spireme-f ormation is accompanied by a definite, 

 although relatively smaller increase in size of the cell. Thus, activity of 

 growth may be expressed by the ratio between the number of spireme 

 and metaphase stages and the number of nuclei in a given group of cells. 

 By means of this ratio it has been proved that the growth-activity of the 

 periblem is less than that of the plerome, but greater than that of the 

 dermatogen ; also that growth-activity in the central zone is greater than 

 in the periphery, being especially great in the region of the calyptrogen. 

 It is also shown that cell-division is rhythmic, adjacent cells exhibiting 

 successive stages of division. In order to reconcile the unequal growth 

 of the periblem and plerome it is supposed that a sort of sliding growth 

 takes place, whereby some of the outer daughter-cells of the plerome 

 become part of the periblem. Adjustment of the tissues is also facilitated 

 by the plasticity of the cell-walls, which enables them to alter their shape 

 in accordance with varying pressures and tensions, while the closely 

 packed cells of the hypodermis and epidermis act as an external support 

 to the cell-displacement. This theory as to the sliding-growth of meri- 

 stematic tissues is in accordance with the periclinal growth of Sachs' 

 theory. 



Lactiferous Vessels and Cells.j — R. Koketsu has studied the 

 functions of lactiferous vessels and cells in various Japanese species 

 belonging to the Composite, Cainpanulaceas, Convolvulaceae, Asclepia- 

 daceae, Apocynacea?, Euphorbiaceaa, and Papaveracere. The chief results 

 obtained are as follows : Earlier descriptions of the structure, course and 

 localization of lactiferous vessels and cells are found to be correct. No 

 true anastomosis of unjointed lactiferous vessels is ever found, but the 

 latter traverse the mesophyll without any distinct connexion with 

 neighbouring cells, and often end blindly. The sieve-tubes of fleshy 

 organs sometimes exhibit a reduction in the number of sieve-plates, 

 although frequently both the conducting parenchyma and the sheath of 

 the vascular bundle is quite normal, while the lactiferous system is most 

 highly developed. The chief lactiferous vessels usually occur in storage- 

 tissue and are often surrounded by epithelial cells, so that it is probable 

 that the lactic fluid is formed at the expense of the organic compounds 

 contained in the storage-tissue. Flowers and their bracts and peduncles 

 have a specialized lactiferous system. 



The lactic fluid is of a viscous nature, especially when highly 

 emulsified ; the taste is unpleasant. It is more or less acid and contains 

 a variable amount of sugar and albumen, but the chief constituents 

 appear to be caoutchouc, resin, or similar substances ; the most abundant 

 inorganic constituents are magnesium and potassium, and peroxidases 

 are common. In addition to the lactic fluid the vessels and cells also 

 contain protoplasm and nuclei, while leucoplasts are not uncommon. 



The author is unable to find any reason for regarding the lactic fluid 



* Ber. Deutsch. Bot. Gesell., xxxii. (1914) pp. 77-83 (3 figs.). 



t Journ. Coll. Sci. Tokio, xxxv. (1913) pp. 1-57 (3 pis. and 2 figs.). 



