630 SUMMARY OF CURRENT RESEARCHES RELATING TO 



has lately investigated the phenomenon afresh, and communicated his 

 results to the St. Petersburg Academy. 



Since the observations as to the nature of the growth had to be 

 made chiefly in continuous darkness, only those plants were suitable 

 whose stems are qualified by their rich provision of nutriment (bul- 

 bous plants) to grow a long time regularly in the dark. The experi- 

 ments were, therefore, chiefly made with Gesneria tubijlora. The 

 growths were automatically measured and recorded by means of 

 apparatus which the author describes. The temperature prevailing 

 during the observation was either read ofi" from a thermometer in the 

 neighbourhood of the plant, or registered every hour by a thermo- 

 grajih. The space in which the plants were kept was so completely 

 darkened that the eye, even after a long stay, received no impression 

 of light, and care was taken to have as favourable and uniform condi- 

 tions of growth as possible. 



It appeared, then, quite unmistakably, that the growth in length 

 of the stems has a periodicity quite independent of the direct action of 

 external agents ; it is diiferently manifested in different plants, but 

 always well marked. Even in perfect darkness the plants experi- 

 mented with showed a periodically increased and diminished growth, 

 such that in the course of every six hours a maximum and minimum 

 occurred. This periodicity was commonly, in the first days after the 

 darkening, very regular, and, as the curve of temperature shows, quite 

 independent of temperature as well as of the direct action of light, 

 which, indeed, was excluded in the experiments. After two or three 

 days, however, the regularity of the jjeriodicity was lost, inasmuch as, 

 while the energy of the growth was commonly increased, the amounts 

 of the daily variation were diminished, and secondary variations 

 appeared, which soon so far took the upper hand over the weakened 

 daily periods that these were at length quite masked and unrecogniz- 

 able. These secondary variations were in their occurrence and 

 duration very regular, and appeared to be due to causes which are in 

 the internal organization of the plant, and therefore always active. 

 Only the active factor which produces the daily period of growth is 

 capable, so long as it is in full activity, of ruling and suppressing these 

 secondary variations. 



A comparison of the position of the maxima in the growth-curves 

 of Gesneria shows that the period is not a 24-hours one ; the duration 

 of the separate periods in different individuals rather varied between 

 16 and 20 hours, whereas in one and the same plant-stem it was 

 within narrower limits, and often remained unchanged several days. 

 Obviously, the maxima must thus be disjilaced relatively to the hours 

 of the day ; generally their appearance was dei)endent on that of the 

 first maximum, which they followed in the given epochs. Other 

 plants showed other periods, but their course was similar to that in 

 Gesneria. 



As to the natural origin of this demonstrated independent perio- 

 dicity of growth, Baranetzky altogether adopts the view given by Pfefter 

 for the periodic movement of leaves. Pfctt'er showed (he says) that if 

 a plant which has ceased from its i)eriodical leaf-motions, in conse- 



