269 



Goeppert (1871), more than forty years after his first 

 observations, undertook a new series of experiments which 

 led him again to the conchision that it is during freezing 

 and not during thawing that the phints are killed. He put 

 to freeze orchids which contain indican and turn blue at 

 death {Calauthe) ; he found that the blue color appeared 

 in the frozen state before thawing. 



Prillieux (1872) repeated these experiments and came 

 to the conclusion that the indican plants became blue only 

 after thawing. It seems that the ditferent conclusions 

 reached by these two authors are due partly to a dis- 

 agreement on what is called blue. Before thawing the 

 plants are of a steel blue color (Stahlblau) and after 

 thawing they are of a deep dark blue. 



Kunisch (1880), instead of utilizing the change of color 

 of indican plants at death, tried to revive them and to put 

 them to grow after freezing and slow thawing but he 

 registered only negative results. 



Miiller-Thurgau (1880) also experimented with indican 

 plants. Using the petals of PJiajus, he could observe by 

 a slow lowering of the temperature that the change in 

 color took place during freezing, not however at the freez- 

 ing point but when, after some ice formation, the temper- 

 ature dropped to a lower level. Any attempt to keep 

 alive by slow thawing petals which had turned blue on 

 freezing failed. The same author (1886) summarizing 

 the results of other experiments in which he subjected 

 "several hundreds" of frozen plants to rapid or slow 

 thawing at various temperatures (for example, potatoes 

 thawed in sand at 45" and at 0") concludes that there is 

 no evidence that slow thawing ever saved these plants 

 from death. However, a few years later (1894), he found 

 that frozen pears and apples show considerable injury aft- 

 er thawing in water at 0° or in luke-warm water, whereas 

 they show only slight or no injury if thawed more slowly 

 in air at 0° or at 20°. (One might mention here that Miil- 

 ler-Thurgau pointed out the error made by previous in- 



