ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 665 



nucleus in certain pines, and finds the phenomena to agree in essential 

 points in the species examined, viz. — Pinus Strobus, P. austriaca, P. 

 rigida, P. montana var. uncinata, and P. resinosa. 



In these species a period of about 13 months elapses between pollina- 

 tion and impregnation. The pollen-grain germinates very soon after 

 pollination, and the vegetative nucleus immediately passes into the 

 pollen-tube. In P. Strobus and austriaca the division of the antheridial 

 cell takes place before the beginning of winter. During the first season 

 the tube grows very slowly ; it may be broad and irregular in outline, 

 or it may branch freely. Shortly before impregnation the generative 

 cell, followed by the pedicel-cell, moves into the pollen-tube ; the 

 pedicel-cell soon passes the generative cell, and takes up a position near 

 the generative nucleus. The generative cell is never limited by a well- 

 defined cell-wall ; it consists, at the time of its division, of an irregular 

 protoplasmic body, in the upper part of which lies the nucleus. In the 

 division of the generative nucleus the spindle is extra-nuclear and uni- 

 polar in origin. This division takes place a little more than a year after 

 pollination, and from a week to ten days before impregnation. Two 

 sperm-cells are never formed ; but the two sperm-nuclei, very unequal in 

 size, remain surrounded by a common mass of protoplasm ; they rapidly 

 attain their full size, the larger one being always in advance. At 

 the time when the sperm-nuclei come into contact, or nearly so, the 

 pollen-tube has penetrated but little, if at all, beyond the nucellar tissue 

 of the first year's growth ; it now begins to elongate, and its downward 

 course through the new nucellar tissue is very rapid. When just above 

 the oosphere, the apex of the pollen-tube is filled with cytoplasm. The 

 vegetative nucleus lies in the upper part of this cytoplasm, and near it 

 is seen the pedicel-cell, still in contact with the lower portion of the 

 cytoplasm which surrounds the sperm-nuclei. No individualised centro- 

 some was observed. 



A copious bibliography is appended. 



(2) Nutrition and Growth (including- Germination, 

 and Movements of Fluids). 



Vitality of Seeds. * — H. H. Dixon finds that seeds of a number of 

 different plants will resist very high temperatures if they are first air- 

 dried. The most resistant seed experimented on was that of Medicago 

 sativa ; after exposure of one hour to 110° C, and then of one hour to 

 121° C, 10 p.c. of the seeds germinated. With other seeds the maximum 

 temperature resisted was from 100° to 110° C. In all cases exposure to 

 a very high temperature resulted in a retardation of germination and 

 extremely slow growth afterwards, the plants being frequently weakly. 

 With regard to the action of poisons on seeds, some seem to be able to 

 withstand it, while others do not. The power of some seeds to resist 

 poisons does not appear to be due to the quiescent state or stability of 

 the protoplasm, but to the imperviousness of the seed-coat. 



Influence of the Solar Rays on the Germination of Seeds.f — 

 According to T. Tammes, the direct rays of the sun, which have such a 



* Nature, lxiv. (1901) pp. 256-7. Cf. this Journal, 1900, p. 302. 

 t Landwirthsch. Jahrb., xxix. (1900) pp. 467-82. See Bot. CentralbL, lxxxvii. 

 (1901) p. 14. 



