ON THE HIBERNATION OF LEMNACE.E. 37 



With regnrd to tbe changes which take place in the winter in the 

 foliation of the Lemnacece, Schleiden* was the first writer who pub- 

 lished detailed investigations. According to him all the species sur- 

 vived the winter by means of special buds, which in the aiituran dropped 

 to the bottom of the ditches, and regained the surface in the spring. 

 These buds M'ere supposed to be destitute of roots, and of a closer and 

 more fleshy tissue than the summer leaves, and became spontaneously 

 detached from the parent-leaf. In S. polyrrhiza this latter remained 

 on the surface of the water, while in the other species it was dragged 

 with its offspring to the bottom. The researches of Schleiden were 

 taken up by Hoffmann, f whose attention was specially directed to 7F. 

 arrhiza, where he detected also leaves specially adapted for the winter. 

 He thns summed up the results of his observations on the tribe. 1. 

 In the whole of them the winter buds are destitute of roots, which is 

 often also the case with those of L. viuior, ])roduced in summer. 2. 

 'i'lie winter buds descend to the bottom in the autumn, pass the winter 

 buried in tlie mud, and ascend again in the spring. 3. In L. polyr- 

 rhiza, the winter buds are very different from those which are produced 

 in the summer; while in L. arrhiza the difference is inconsiderable, 

 but still very characteristic. 4. In L. minor and gibba, which often 

 pass the winter on the surface, the form of the buds offers scarcely any 

 difference. 5. Finally, as respects L. i?-isulca, Hoffmann states that 

 the relations between the two kinds of leaves are more difficult to ob- 

 serve, because their connection is closer, and it is only flowering plants 

 which float on the surface. The same subject has, finally, been fol- 

 lowed out by Hegelmaier, who differs from some of the observations 

 of his predecessors. In L. minor and S. trisulca he was unable to de- 

 tect the production of leaves specially adapted for winter. He con- 

 firmed Schleiden's observations with respect to *S'. polyrrliiza, and de- 

 scribed, with greater exactness, the hibernation of IF. arrhiza. The 

 following are M. Van Iloren's observations more in detail : — 



Sjairodela polyrrhiza. At the approach of winter, individuals of this 

 species produce usually leaves of a new form, which are known as 

 winter-leaves. The date of their production varies with the locality ; 

 in general, plants growing in very favourable conditions produce them 

 towards the end of August or in September; in exposed places or 



* ' Linnsea,' 1839 ; also in his 'Beitriige zur Botanik,' 1844. 

 t ' Aniialcs des Sciences Naturelles,' 2iKle seric, t. 14. 



