386 True. — On the Influence of Sudden Changes of 
a more or less prolonged period of retardation of the growth- 
rate. The cause of the retardation was not demonstrated, but 
is probably due. in part, to decrease of the turgor-pressure, 
and, in part, to a sensitive reaction following the irritation of 
the living organisms. 
(2) A sudden and decided decrease of the concentration of 
the medium causes a change of turgor-pressure producing 
a mechanical elongation, also a more or less prolonged period 
of retardation of growth. The cause of the retardation is 
found in a sensitive reaction of the living organisms to the 
change of medium. Since a reduction of growth is found to 
accompany both an increase and a decrease of turgor-pressure, 
it follows that growth and turgor-pressure here stand in no 
directly proportional relation to each other. 
II. The Effect of Sudden Changes of Temperature. 
Historical. 
Although a number of earlier investigators 1 had studied 
the effects of sudden temperature changes on the streaming of 
protoplasm, Koeppen 2 first investigated the effect exerted on 
plant-growth. He concluded that the act of change brought 
about a reduction of growth in radicles of various seedlings. 
Sachs 3 , from observations on the growth of certain etiolated 
stems, was unable to confirm this view. 
Pedersen’s 4 results led him also to take exception to 
Koeppen’s generalization. He exposed roots of seedlings of 
1 Max Schultze, Protoplasma der Rhizopoden nnd der Pflanzenzelle, 1863, 
p. 63. Dutrochet, Comptes Rendus, 1837, T. V, p. 777 ff- Hofmeister, Pflan- 
zenzelle, 1867, pp. 4 7 and 53. See also Sachs, Handbuch der Experimental- 
Physiologie der Pflanzen, 1865, p. 69. 
2 Koeppen, Warme und Pflanzenwachsthum. Dissertation, Moskau, 1870, 
pp. 20 and 22. 
3 Sachs, Ueber den Einfluss der Lufttemperatur und des Tageslichts auf die 
stiindlichen und taglichen Anderungen des Langenwachsthums der Internodien. 
Arb. d. bot. Inst, in Wurzburg, 1872, Heft II, p. 164. Also, Gesammelte 
Abhandlungen fiber Pflanzenphysiologie, Bd. II, p. 677. 
4 Pedersen, Haben Temperaturschwankungen einen ungiinstigen Einfluss auf 
das Wachsthum ? Arb. d. bot. Inst, in Wurzburg, Bd. I (1874), p. 563. 
