om 
EN ee 
” 
\ 

PHYSIOLOGICAL STIMULI AND ITS SIGNIFICANCE 263 
which will come into flower in the next year, is thus expressed by 
Blaauw (1920): „It is certain, that the after-effect of the preparation 
not only is felt in the warm period itself, but also causes, after that 
period, an initial acceleration of the processes, as compared with the 
non-treated ones”. „One should keep in mind, that the drying of the 
bulb (by the loose of its roots and the taking up), means the end of its 
leafforming period....” (p. 59). 
If we now compare the abnormal conditions, under which the Oeno- 
thera’ s with which one experiments, are cultivated we find a certain si- 
milarity between these and the conditions caused, in the case of Hya- 
cinthus orientalis, by the taking up of the bulbs while still in an unripe 
condition: in both cases the vegetationperiod is shortened and accelerated. 
I should like to call attention in this connexion, to what VAN OVEREEM 
. (1920) says about this point, on pp. 12 and 13. He says that the forma- 
tion of the stem takes place at different times in the case of different 
species, and that he, following in this respect, the method of DE VRIES 
cuts away the lateral branches. This favors the seedproduction. „Dieser 
Zustand”, he continues, „ist aber für die Pflanze anormal und viele an- 
dere Forscher (z. B. Davis, LoTsy befolgen, nach ihren Abbildungen zu 
urteilen, diese Methode nicht. Für meine Pflanzen war sie notwendig, 
weil die Samenbildung bei vielen dieser abweichenden Formen gering 
ist. Von den gigas-Rosetten wurden bei üppiger Entwickelung stets 
viele Blätter weggeschnitten, wodurch das Schiessen befördert wird. 
Nach der Stengelbildung wurde das Begiessen ausgesetzt”. Further- 
more, VAN OVEREEM (1922 p. 19) says, referring especially to Oenothe- 
ya Lamarckiana gigas, supposed to be more decidedly biannual than 
O. Lamarckiana,: „Dieser Zweijährigheit kann man durch verschiede- 
ne Mittel, welche im Gartenbau wohlbekannt sind (Verpflanzen, Ab- 
schneiden van einem Teil der Rosettenblätter) vorbeugen”. 
From this and from what is further known, about the cultivation of 
the Oenothera’s, it follows, that they are frequently cultivated under abnor- 
mal conditions, conditions which are especially directed towards the end, 
to force, these, usually biannual, plants to flower in the first year. Cutting 
away of a part of the leaves of the leafrosette may contribute to this, 
just as in the case of the hyacinth, the cutting off of the green leaves 
(= harvesting in unripe condition) puts a stop to the leaf-forming peri- 
od of the vegetationpoint and makes it enter earlier into the period of 
flower-formation, which it accelerates moreover. But also in those cases 
