220 



WINTERING HABITS 



[CH. 



in the spring they expand into graceful shoots (Fig. 145, p. 222). 

 The germination normally occurs in March or April, but it can be 

 induced at any time if the temperature is favourable; if brought 

 indoors and kept warm, the turions will develop into-new plants 

 in October, November, December or January^. Cold is ini- 

 mical to the winter-buds, and, if frozen for a few days, many of 

 them are killed. The turions of different aquatics vary very 

 widely in their capacity to withstand freezing^. Those of Utricu- 

 laria vulgaris are uninjured by inclusion in ice for as long as 

 twelve days, while Hydrocharis Morsus-ranae^ according to 

 Gliick's experiments, is still more sensitive than Myrio-phyllum^ 



Fig. 143. Utricularia intermedia, Hayne. A, winter-bud leaf (enlarged). 

 B, summer leaf (less enlarged). [Goebel, K. (1891-1893).] 



for, after three to ten days in ice, nearly all the turions were 

 killed. However, according to Guppy^, they are able to with- 

 stand inclusion in ice for a period of some weeks; the discre- 

 pancy between these results requires some explanation, which 

 may perhaps lie in the particular conditions of the experiments. 

 The turions of many hydrophytes are saved from the risk of 

 becoming frozen by their habit of wintering at the bottom of 

 fairly deep water. 



For many years botanists were inclined to interpret the 

 development of ' winter-buds ' on the simplest teleological 



1 Cluck, H. (1906). 2 Guppy, H. B. (1893). 



