476 
SUMMARY OP CURRENT RESEARCHES RELATING TO 
of leaves is dependent, on tlie one hand, on the degree of moisture of 
the air, on the other hand on the chemical intensity of the light. 
Very sensitive parts of plants ( Amaranthus melancholicus ) exhibit 
heliotropism when exposed to light amounting only to a fraction of a 
millionth of Bunsen and Roscoe’s unity of intensity ; in the case of 
etiolated stems of Vicia sativa to only a ten-millionth. Helio tropic 
organs may either suspend their growth entirely in the dark, as the 
hypocotyl of Viscum album , or their growth may be promoted, as in the 
case of ordinary positively heliotropic organs, or retarded, as the coty- 
ledons of Pinus sylvestris, or the intensity of growth may be nearly the 
same in the dark as in the light, as the cotyledons of Abies excelsa. 
Influence of Phosphorus on the Growth of Plants.* — By a series 
of experiments on Tradescantia Selloi , Dr. F. Noll claims to have 
determined that phosphorus is of great importance to the growth of 
plants, not only for the seeds but also for the formation of the vegetative 
organs. 
Morphology and Physiology of Grafting.^ — As the result of a 
series of experiments on the grafting of annual, biennial, and perennial 
plants, M. L. Daniel states that grafting often succeeds between genera 
belonging to different sub-tribes, or even to different tribes of the same 
family. In herbaceous plants, root-grafting is especially successful. 
Annual or biennial, grafted on perennial plants, remain respectively 
annual or biennial. The host and the graft exercise a reciprocal influ- 
ence on one another ; but if seeds from a root-graft germinate the seed- 
lings display a return to the original properties of the grafted species. 
Reserve-materials accumulated in a root-host before grafting are 
rarely used by the graft, unless it belongs to the same family as the 
host. When the graft is first made, the passage of the crude sap from 
the host is effected only with great difficulty. The absorption of water 
is reduced without any decrease in the transpiration. The passage of 
sugar, starch, and other substances between the host and the graft is 
subject to different laws in different cases. 
Germination of Seeds. — The late G. J. Romanes f carried out 
a series of experiments for the purpose of determining the extent to 
which the power of germination of dry seeds is affected by preventing 
their respiration for long periods. To this end they were sealed in 
vacuum-tubes of high exhaustion (one-millionth of an atmosphere) for 
three months, and then transferred, for a period of twelve months, to 
other tubes containing pure gases or vapours (carbon dioxide, nitrogen, 
chloroform, &c.). In no case was their power of germination deteriorated 
to any considerable extent. 
M. R. Pictet § states that many seeds may be exposed, when dry, to 
a temperature of — 200°, without in the least injuring their vital activity. 
Similar results were obtained with various bacteria. 
According to M. C. Chauveaud, || the germination of grape-seeds can 
* Naturwiss. Wochenschr., viii. (1893). See Biol. Centralbl., xiv. (1894) p. 258. 
| Rev. Gen. de Bot. (Bonnier), vi. (1894) pp. 5-21, 60-75 (2 pis.). Of. this 
Journal, 1893, p. 211. % Proc. Roy. Soc., liv. (1894) pp. 325-7. 
§ Arch. Sci. Phvs. et Nat., xxx. (1893) pp. 293-314. 
|| Comptes Rendus, cxviii. (1894) pp. 211-2. 
