914 SUMMARY OF CURRENT RESEARCHES RELATING TO 



He finds that it has no haustoria, and is no true parasite, but a sapro- 

 phyte, i. e, a non-chlorophyllaceous plant growing in humus. The 

 root-fibres appear to be invariably clothed with a dense weft consisting 

 of the mycelium of a fungus, which covers the extremities of the fibres 

 like a cap ; it is not, however, parasitic upon the root. The parasitic 

 nature of Monotropa has been wrongly inferred from the fact that its 

 roots often coalesce in their growth with roots of the firs beneath 

 which it grows that have become deformed and partially destroyed by 

 a parasitic fungus. 



Influence of Light on Germination.* — Dr. Stebler states, as the 

 result of a series of observations, that in the case of certain seeds, 

 especially of grasses, light promotes their germination, while in the 

 dark they either do not germinate at all or only with difiiculty. This 

 was observed in the seeds of Festuca, Cynosurus, Alopeciirus, Holcus, 

 Dactylis, Agrostis, Aira, AntJioxanihum, &c. In the case of seeds 

 which germinate easily and rapidly, like those of peas, beans, clover, 

 &c., he was unable to detect that light had any advantageous 

 influence. 



Influence of Intermittent Light on the Formation of Chloro- 

 phyll.! — Wiesner considers that the formation of chlorophyll by the 

 action of light is a photo-chemical inductive process, because the 

 exposure for 2^ minutes of etiolated barley and oat seedlings to con- 

 tinuous light did not result in the formation of chlorophyll, but when, 

 after a dark interval, light was again allowed to act, then chlorophyll 

 was produced. The effect of the light was, therefore, to induce the 

 formation only, as at the end of a single period of illumination no 

 more chlorophyll was observable than at the beginning. Again, with 

 continuous illumination, the first trace of chlorophyll was only 

 observable after five minutes. Long-continued illumination, and 

 illumination in excess, will, however, give rise to the production of 

 this substance. 



Decomposition of Nitrates by Plants in the Dark.| — It is well 

 known that green plants grown in the dark do not increase in weight, 

 owing to their want of power to decompose the carbonic acid in the 

 air. Boussingault has found that when seeds are sown in the dark in 

 soil containing nitrates, they do partially decompose these nitrates. 



Influence of Gravitation on Plants.§ — F. Elfving has tried further 

 experiments on the influence of gravitation on positively and nega- 

 tively heliotropic organs. As an instance of the latter he took 

 Phycomyces nitens, and found that, when the position was reversed, 

 growth in length was retarded by gravitation. This effect can be 

 observed directly, or by the secondary result when the plant is 

 restored to its normal position. The next experiments were for the 

 purpose of ascertaining whether gravitation exercises any influence on 



* Verhandl. naturwiss.Vereins Zurich, 1881. See Bot. Ztg.,xxxix. (1881) p. 469. 

 t Journ. Chem. Soc. Abstr., xl. (1881) p. 930, from Bied. Centr., 1881, p. 352. 

 t Ann. Chem. et Phys., xxii. (1881) p. 433. See Naturforscher, xiv. (1881) 

 p. 237. 



§ Acta Soc. Scient. Fenn., xii. (1880). See Bot. Ztg., xxxix. (1881) p. 176. 



