VENUS' S FLYTRAP AND THE BLADDERWORTS 61 



siderable number of them are in contact with it. The presence of the 

 insect not only stimulates the hairs to bend inward but also to 

 secrete protein-digesting enzymes. The digestible portions of the 

 insect are thus rendered soluble and are absorbed by the leaf as food. 

 After the insect has been digested the secretion of enzymes ceases, 

 the hairs slowly bend back to their former positions, and the leaf 

 is ready for the next victim. It is interesting to note that inorganic 

 bodies, such as particles of sand, or anything not containing pro- 

 teins, do not stimulate the hairs to secrete enzymes or to move in 

 any way. 



Quite comparable to the sundews so far as symbiosis is concerned, 

 although belonging to a different family of plants, are the butter- 

 worts, or Pinguicidas. Pinguicula vulgaris grows on wet limestone 

 rocks in the extreme northern part of the United States and in 

 Canada. It is a small plant with a rosette of sessile, entire, spatulate 

 or somewhat elliptical leaves, and sends up in early summer a scape 

 with one violet-colored flower. The leaves are soft-fleshy and rather 

 greasy to the touch, which accounts for both its Latin and common 

 names. On the upper surface of the leaf are scattered glandular 

 hairs to which insects adhere as in the sundew. When an insect is 

 caught the hairs do not move as in the sundew but the edge of the 

 leaf curves inward in such a way as to bring several hairs in contact 

 with the insect. Between the glandular hairs are some shorter 

 papillate or disk-like hairs which probably have the function of 

 absorbing the digested proteins. 



39. Venus's Flytrap and the Bladderworts.— Venus's flytrap 

 (Dionaea muscipida) is a rather rare little plant that grows on wet 

 sand in several places in North and South Carolina (Fig. 23). It 

 has a rosette of leaves each of which possesses at its terminal end 

 two oval-shaped lobes w^hich are hinged together at the mid-rib and 

 have long stiff teeth around the outer edge. On the upper surface 

 of each lobe are three bristle-like hairs which are very sensitive. 

 ^Yhen one of these hairs is touched the lobes close suddenly like a 

 trap. If an insect touches one of the hairs, therefore, it is almost 

 invariably caught in the trap. The stiff teeth along the edges of the 

 trap interlock like the teeth of a bear trap and the two lobes press 

 together with such force that the outline of the insect can often be 

 seen from the outside. The insect is digested by protein-digesting 

 enzymes, secreted by glands on the surfaces of the leaves, and the 

 digested portions are absorbed by the leaf. The trap then slowly 



