878 PINGUICULA VULGARIS. Chap. XVI. 



complete re-expansion in 16 hrs. 30 m. Nitrogenous 

 fluids act for a shorter time than nitrogenous sub- 

 stances ; thus, when drops of an infusion of raw meat 

 were placed on the midrib of a leaf, the incurvefl 

 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 over- 

 lapping margin are thus brought into contact with 

 such objects and pour forth their secretion, afterwards 

 absorbing the digested matter. But as the incurvation 

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

 only slight importance, yet perhaps greater than at 

 first appears. 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 interval) found some of 

 them quite washed away, and many others safely 

 tucked under the now closely inflected margins, the 

 glands of which all round the insects were no doubt 

 secreting. We can thus, also, understand how it is 

 that so many insects, and fragments of insects, are 

 generally found lying within the incurved margins 

 of the leaves. 



The incurvation of the margin, due to the presence 

 of an exciting object, must be serviceable in another 



