306 PINGUICULA VULGARIS. [Chap. XVL 



ments of glass cause little or no secretion, and yet excite 

 movement: whereas a strong solution of carbonate of am- 

 monia quickly excites copious secretion, but no movement. 



One of the most curious facts with respect to the move- 

 ment of the leaves is the short time during which they 

 remain incurved, although the exciting object is left on 

 them. In the majority of cases there was well-marked re- 

 expansion within 24 hrs. from the time when even large 

 pieces of meat, &c., were placed on the leaves, and in all cases 

 within 48 hrs. In one instance the margin of a leaf re- 

 mained for 32 hrs. closely inflected round thin fibres of meat; 

 in another instance, when a bit of sponge, soaked in a strong 

 infusion of raw meat, had been applied to a leaf, the margin 

 began to unfold in 35 hrs. Fragments of glass keep the 

 margin incurved for a shorter time than do nitrogenous 

 botlies; for in the former case there was complete re-expan- 

 sion in 16 hrs. 30 m. Nitrogenous fluids act for a shorter 

 time than nitrogenous substances; thus, when drops of an 

 infusion of raw meat were placed on the midrib of a leaf, 

 the incurved margins began to unfold in only 10 hrs. 37 m., 

 and this was the quickest act of re-expansion observed by 

 me ; but it may have" been partly due to the distance of the 

 margins from the midrib where the drops lay. 



We are naturally led to inquire what is the use of this 

 movement which lasts for so short a time? If very small 

 objects, such as fibres of meat, or moderately small objects, 

 such as little flies or cabbage-seeds, are placed close to the 

 margin, they are either completely or partially embraced by 

 it. The glands of the overlapping margin are thus brought 

 into contact with such objects and pour forth their secretion, 

 afterwards absorbing the digested matter. But as the in- 

 curvation lasts for so short a time, any such benefit can be of 

 only slight importance, yet perhaps greater than at first ap- 

 pears. The plant lives in humid districts, and the insects 

 which adhere to all parts of the leaf are washed by every 

 heavy shower of rain into the narrow channel formed by the 

 naturally incurved edges. For instance, my friend in 

 North Wales placed several insects on some leaves, and two 

 days afterwards (there having been heavy rain in the inter- 

 val) found some of them quite washed away, and many oth- 

 ers safely tucked under the now closely inflected margins, the 



