ZOOLOGY AND BOTANY, MICliOSCOPY, ETC. 179 



Absorption of Phosphoric Acid by Plants.* — Experiments made by 

 1>. Prianischnikow as to the absorption of phosphoric acid by plants 

 from salts which are only slightly soluble, showed that different plants 

 exhibit different capacities in this respect. The tricalcium phosphate 

 of bones is assimilated much more readily than when the phosphorus 

 is presented in the form of apatite or phosphorite ; but the form of 

 phosphoric acid which is most readily taken up by the higher plants 

 is that of freshly precipitated tricalcium phosphate which contains 

 water of crystallisation. 



Germination of Hsenianthus tigrinus.t — Prof. F. Hildebrand de- 

 scribes the remarkable phenomena exhibited by this plant aud other 

 species of the genus, belonging to the Amaryllideae. When the fleshy 

 berry bursts, the seeds do not fall to the ground, but remain attached 

 to the open pericarp by very long and extremely elastic mucilaginous 

 threads, which may attain a length of 20 cm., and which are the result 

 of the disintegration of the septa of the ovary. When a bird attacks 

 the fleshy berry, the seeds still remain attached to its beak by these 

 elastic threads ; and, in getting rid of them, it carries the seeds to a 

 considerable distance. The germination of the seeds and the early 

 growth of the plant present several interesting peculiarities. The seeds 

 will not germinate unless they are freed from the seed-vessel. The 

 bulbs continue to grow for some time after the commencement of ger- 

 mination, and may increase their size several fold before the appearance 

 of the flower-stalk. 



(3) Irritability. 



Geotropic Sensitiveness of the Root-tip.t — F. Czapek replies at 

 length to Wachtel's § criticisms on his previous observations, and gives 

 the results of fresh experiments which support the correctness of 

 1 )arwin's ascription of a " brain-function " to the apex of the root. He 

 states, however, that too sharp a distinction is often drawn between the 

 root-apex and the zone of growth. Even the apical 2 mm , which are 

 the seat of the geotropic sensitiveness, may, under all circumstances, 

 exhibit a not inconsiderable growth, although a zone of 1 mm. lying 

 behind the apical 2 mm. displays a very much greater power of growth, 

 aud may be termed the zone of maximum growth. 



Irritability of the Stamens of Berberis.|] — A. TJsteri gives a resume 

 of the published observations regarding the movements of the stamens 

 of Berberis when touched by an insect or other exciting cause. His 

 own observation leads him to the conclusion that the effect of the 

 irritability is to throw the pollen on to that part of the insect which 

 will come into contact with the stigma of the next flower it visits. 



Nature of the Stimulus which causes the Change of Form in 

 Polymorphic Green Algge.^ — From experiments on a form of Stigeo- 

 clonium (probably S. tenue), B. E. Livingston draws the general con- 



* Ber. Deutsch. Bot. Ges., xviii. (1900) pp. 411-6. 



t Tom. cit., pp. 372-85 (1 pi.). 



t Prinssheim's Jahrb. f. wies. Bot., xxxv. (1900) pp. 313-05. 



§ Cf. this Journal, 1899, p. 621. 



II Helios, 1900, p. 49. See Bot. Centralbl., Ixxxiv. (1900) p. 228. 



«j Bot. Gazette, xxx. (1900) pp. 289-317 (2 pis.). 



N 2 



