780 



is completely at variance with these facts. In the tirst place so far 

 as concerns the positive or negative inflnence of light. The general 

 conception, supported by numerous facts, is that light in general 

 exercises a retarding intluence on growtii. In Pfeffkr's Pflanzen- 

 [}hysioJogiè (2e Aufl. 1904, Bd. II. biz. 108) as a result of facts then 

 known this conception is thus formulated : "Innerhalb der zuUissigen 

 Lichtgrenzen wird, so weit bekannt, in der phototonischen Ptlanze 

 durch Verminderung der Beleuchtung eine gewisse Beschleuniging, 

 durch Zunahme der Helligkeit eine gewisse Verlangsamung der 

 Zuwachsbewegung bewirkt". 



In particular this was also deduced from the experiments of Vines 

 {Arh. WUrzbuni Tl, 1878), who observed the growtii of the sporangio- 

 pliores of Phycomyces every hour or half hour in daylight and in 

 the dark and found a slightly smaller growth in the light period 

 than in the dark. In this investigation, as in that of others, too hxrge 

 and too indetinite quantities of light were used ; moreover most 

 investigators, including Vines, used intermittent stimulation, for 

 which reason the intlueiice of illumination made itself felt as an 

 after effect also in the dark periods and conversely. Further in Vines' 

 experiments the temperature is very variable, in some it changed 

 for example from 227,° C\-26° C. 



Whilst nearly all earlier investigators found a smaller growth 

 in the light than in the dark, Helene Jacobi {Sitzunysber. cL K. Ak. 

 (I IF. z. Wien, Abt. I, Bd. 120, 1911^ made the statement that, 

 for example, plants of Tritlcum and Pha.^eohis, which had been 

 illuminated 24 hours before for a fairly short time, had become 

 slightly larger, than the non-illuminated controls. In this investigation, 

 however, the growth was not measured until 24 hours later and 

 then only with the naked eye, whilst the humidity and the tempe- 

 rature varied very greatly during many experiments. In comparison 

 with this Vines' investigation of 1878 may almost be called modern, 

 for he worked with a telesco[)e, ensured a fairly constant humidity 

 and did not wait for 24 hours before taking his readings. 



Further more the representation in the literature of the nature of 

 the growth reaction induced by light is at variance with the above 

 facts. The current conception of this nature is summarised by Peeffer 

 as follows (biz. 109): "Selbst bei dem Uebergang von einer hellen 

 Beleuchtung zu voller Finsterniss, oder umgekehrt, wird die Wachs- 

 thumsschnelligkeit gewöhnlich nur um 5 — 30 7o» selten um 50 7o 

 oder mehr beschleunigt, resp. verlangsamt, und bei schwacherem 

 Beleuchtungswechsel liisst sich eine Reaktion nicht immer nach- 

 weisen". Pfeffer further indicates, that a change in the rate of 



