192 SUMMARY OF CURRENT RESEARCHES RELATING TO 



stage this thread is drawn round so as to form a double thread, the two 

 parts of which intertwine during the succeeding stage and give rise to a 

 double chromosome. The reduced number of chromosomes is about 

 thirty. The stigma and upper part of the style has an endotrophic 

 conducting tissue, while the rest of the pistil has an ectotrophic con- 

 ducting tissue, which is distributed over the placenta, but only forms a 

 narrow band on the side near each carpel. The upper surface of the 

 placenta is swollen between the points of insertion of the seeds ; this 

 arrangement, together with the conducting tissues, serves to direct the 

 right course of the pollen-tube. While the nuclei are in the pollen-tube 

 no special sheath could be seen surrounding them, but when they reach 

 the embryo-sac a bladder-like sheath is visible, which soon disappears. 

 The pollen-tube discharges its contents into the single synergid. After 

 the division of the central nucleus the embryo-sac divides up into smaller 

 cells round the antipodals, and these small cells fill up the remaining 

 space. Two kinds of endosperm are formed : a basal portion which 

 develops quickly, and a central portion which develops later at the 

 expense of the basal portion. The nucellus-tissue is rich in starch and 

 forms a perisperm during the development of the endosperm ; it has quite 

 disappeared, however, in the ripe seed. Fats and proteids are found in 

 small quantities in the basal endosperm and in the embryo, but in larger 

 quantities in the central endosperm. Starch is found in the embryo. 

 While the seed is ripening, tubercles grow out from the bases of the 

 funicles, which serve for seed-dispersal. 



Physiology. 

 Nutrition and Growth. 



Biological Chemistry.* — When Raulin published his study of the 

 growth of a mould in an artificial solution he remarked on the advan- 

 tage that seemed to accrue to the fungus from the admixture of certain 

 chemical elements. Maurice Javillier has taken up the subject, and has 

 again proved the favourable influence of infinitesimal quantities of zinc 

 on the growth of Sterigmatocystis nigra. It acts as an antiseptic and 

 prevents the development of foreign organisms that would damage 

 the culture. 



Irritability. 



Sleep-movements of Leaves.f — W. Pfeffer has investigated the 

 sleep-movements of plants, and finds that they are the result of light 

 and heat reactions set up by daily changes in illumination and tempera- 

 ture. The sleep-movements disappear when the temperature and illu- 

 mination are uniform, and never appear in plants raised under such 

 conditions, although by establishing a daily change of light and tem- 

 perature movements reappear in the one case and are induced in the 

 other. Such movements can only be brought about by gradual and not 

 by sudden change, and are the result of internal activities tending to 

 the establishment of a position of equilibrium corresponding to the new 



* Comptes Rendus, cxlv. (1907) pp. 1212-15. 



t Abhandl. Math. Phys. Kl.k. Sachs. Ges. Wiss., xxxiii. (1907) pp. 259-472 (36 

 figs.). 



