548 SUMMARY OP CURRENT RESEARCHES RELATING TO 



Dichogamy* — According to Prof. T. Meehan, dichogamy (proter- 

 andry and proterogyny) has frequently no connection with any provision 

 for aiding cross-fertilization, but is dependent on the different conditions 

 under which the male and female organs of flowers are produced, the 

 male organs requiring, as a rule, a smaller degree of heat for their 

 maturity than the female. 



Fertilization by Snails.j — Hcrr F, Ludwig finds that LeucantTiemim 

 vulgare is pollinated in wet weather, in the absence of the ordinary 

 insect-visitors, by a nocturnal snail, Limax Isevis, attracted by the white 

 ray-ilorets, on which it feeds. 



{;2) Nutrition and Growth, (including Movements of FluidsD. 

 Physiology of Growth. :j: — Herr J. Wortmann gives the details of a 

 number of experiments, chiefly on Butomus umhellatus and Pliaseolus 

 multiflorus, which confirm his previous conclusions that growth is due 

 not merely to the force of turgidity in the cell, but partly to a force 

 located in the cell-wall itself. Among the more important general 

 results obtained are the following. The extensibility of the shoot is 

 greatest at its apex, gradually diminishing thence to the base. In the 

 entire growing region below the point of maximum growth up to that 

 point where growth has ceased, there is no variation in the intensity of 

 the turgidity, at all events not sufficient to have any effect on the 

 growth. The turgidity of the point of maximum growth may therefore 

 be reo"arded as constant. In the region between the terminal bud and 

 the zone of maximum growth there is, in the youngest cells which have 

 not yet begun to elongate, a rapid increase of turgidity, which becomes 

 less marked when the cells begin to elongate, but continues as far as the 

 zone of maximum growth, in which it attains its highest and constant 

 intensity. The production of cell-wall gradually increases from the 

 commencement of growth in length until the period of maximum growth, 

 and then gradually and slowly decreases until it reaches zero in the 

 mature cells. 



From experiments on the growth of seeds of Lepidium, Herr Wort- 

 mann Avas able to confirm the theory of Sachs and de Vries that the 

 growth of the cell and the increase in superficies of the cell-wall depend 

 directly on the intensity of the turgidity and consequent tension of the 

 cell, the latter having for one of its factors the extensibility of the cell- 

 wall. The superficial growth of the cell-wall takes place mainly by 

 apposition, though this is sometimes assisted by intussusception. 



Descending Current of Water.§ — Herr J. Wiesner gives the follow- 

 ing demonstration of the existence of a descending current in plants. 

 If a cut leafy branch of the vine is immersed in water, all the succulent 

 parts swell up from increased turgidity ; but if it is now lifted up so 

 that the leaves are elevated above the water while the apex of the shoot 

 still remains submerged, this latter becomes flaccid, which can be 

 accounted for only by the sap having passed out of it by a descending 

 current into the lower leaves. Although this descending current has not 



* Proc. Acad. Nat. Sci. Philad., 1888, pp. 391-4. 



t SB. Gesell. Naturf. Freunde Berlin, 1889, pp. 16-8. See Bot. Centralbl., 

 xxxvii. (1889) p. 392. 



X Bot. Ztg., xlvii. (1889) pp. 229-39, 245-53, 261-72, 277-88, 293-304 (7 figs.). 

 Cf. this Journal, 1888, p. 615. § Bot. Ztg., slvii. (1889) pp. 1-9, 24-9. 



