xvii] TURIONS 223 



hand, luxuriant specimens growing in water in warm situations 



may vegetate throughout the winter without forming turions. 



It is most Hkely that, in normal Hfe, it is 



the lowering of the temperature in the 



autumn which induces the formation of 



winter-buds. 



That it is unfavourable conditions 

 which bring about the development of 

 turions, seems to be true not only of the 

 Water Milfoil but of aquatics in general. 

 Some remarkable experiments on the effect 

 of starvation upon Utricularia have been 

 quoted on pp. 102103. Similar results 

 have been obtained in the case of Sagittaria 

 sagittijolia}- in which, however, the vege- 

 tative multiplication is effected by tubers 

 and not by turions. Tuber formation in 

 the Arrowhead normally occurs when the 

 plant has exhausted itself by the forma- 

 tion of inflorescences, and when cooler 

 weather sets in. The land form, like that 

 of Myriophylluniy produces tubers several 

 weeks earlier than the form growing under 

 the optimum aquatic conditions. Gluck^, 

 one autumn, planted a tuber of the Arrow- 

 head in a pot of earth and left it there, 

 altnost without water, until towards the 

 end of the following July. The plant, which 

 had failed to appear above the soil, was 

 then examined, and it was found that the 

 tuber had put out a few wretched-looking 

 little ribbon-leaves, which had not possessed strength to pene- 

 trate the earth. It had also formed four tiny stolons, 1-5 to 

 2 cms. long, each terminating in a small tuber, 8 to 10 mm. in 

 length. This tuber formation had apparently occurred as a 



1 Gluck, H. (1905). 



Fig. 146. Myriophyllum 

 verticillatum, L. Land 

 form with five subter- 

 ranean turions, two of 

 which are marked K. 

 The turion of the pre- 

 vious generation, W, is 

 still attached to the base 

 of the plant and has 

 formed a number of 

 adventitious roots. The 

 two lowest turions have 

 grown out of the axis 

 of the previous turion. 

 (Reduced.) [AfterGliick, 

 H. (1906), Wasser- und 

 Sumpfgewachse, Bd. ii, 

 PI. V, fig. 61.] 



