INSECTIVOROUS AND CLIMBING PLANTS. 325 



plants should do, and have a good and true digestion. 

 Pinguicula, or butter wort, is the representative of 

 this family upon land. It gets both its Latin and its 

 English name from the fatty or greasy appearance of 

 the upper face of its broad leaves ; and this appear- 

 ance is due to a dense coat or pile of short-stalked 

 glands, which secrete a colorless and extremely viscid 

 liquid. By this small flies, or whatever may alight or 

 fall upon the leaf, are held fast. These waifs might 

 be useless or even injurious to the plant. Probably 

 Mr. Darwin was the first to ask whether they might 

 be of advantage. He certainly was the first to show 

 that they probably are so. The evidence from experi- 

 ment, shortly summed up, is, that insects alive or dead, 

 and also other nitrogenous bodies, excite these glands 

 to increased secretion ; the secretion then becomes 

 acid, and acquires the power of dissolving solid ani- 

 mal substances — that is, the power of digestion in the 

 manner of Drosera and Dioncea. And the stalks of 

 their glands under the microscope give the same ocu- 

 lar evidence of absorption. The leaves of the butter- 

 wort are apt to have their margins folded inward, like 

 a rim or hem. Taking young and vigorous leaves to 

 which hardly anything had yet adhered, and of which 

 the margins were still flat, Mr. Darwin set within one 

 margin a row of small flies. Fifteen hours afterward 

 this edge was neatly turned inward, partly covering 

 the row of flies, and the surrounding glands were se- 

 creting copiously. The other edge remained flat and 

 unaltered. Then he stuck a fly to the middle of the 

 leaf just below its tip, and soon both margins infold- 

 ed, so as to clasp the object. Many other and varied 



