196 BUDS AND STIPULES 



the Teasel (Dipsacus), where the bases of the petioles 

 are expanded and connate, thus forming a large cup, 

 which generally contains water. It has been suggested 

 by Kerner that this water forms a sort of moat, which 

 protects the flowers from ants and other creeping 

 insects. On the other hand, Mr. Francis Darwin 

 suggests that insects, &c, are drowned in the water, and 

 thus supply the plant with animal food. He has de- 

 scribed certain curious protoplasmic threads, emitted 

 by some of the cells, which he suggests may serve to 

 absorb the nourishment thus supplied. 



As Supports 



It is probable that, as Grevillius (2G) has suggested, 

 the ocrea of Polygonum may be of use in strengthening 

 the stem at the internodes, which are points of rapid 

 growth, and consequently of weakness. He observes 

 that this can be tested by removing the sheath, and then 

 shaking the stem, when it will be found that it is 

 especially liable to give way at the internode. 



