Chapter IX —109— Pinguicula 



that the abundant mucilaginous secretion following application of 

 granules of sugar is without digestive power. 



Having cultivated material of P. vulgaris collected in the mountains 

 of California east of Crescent City, I repeated such experiments as 

 done by Darwin, Goebel and Fenner on about a dozen leaves, with 

 definitely positive results. I cite only one as typical, this being il- 

 lustrated in 15 — I, see also 13 — 6. The total activity extended over 

 more than six days. Four minute flies were observed caught in a row 

 parallel to one margin and two similarly placed with respect to the 

 other margin. Already the one margin was slightly curved upwards 

 on Oct. 2, the other showed no motion until the night of Oct. 3-4. On 

 the morning of Oct. 4 both margins were well curved, enough to hide 

 all the flies. On Oct. 6, the inward rolHng of the margins was well 

 developed, and next day it had begun to recede, again exposing the 

 flies to one's vision. This behavior was typical of the whole series of 

 cases. This and a number of other cases observed seem to throw doubt 

 on the vaHdity of Darwin's statement that the time leaves remain 

 incurved, even though the exciting objects remain in position, is but 

 short, i.e., not more than twenty-four hours. It is further well known 

 that the contact of an insect with the leaf at a point removed from the 

 margin, i.e., near the midrib, results in the dishing of the leaf below 

 the insect (Darwin, Batalin). This, as Batalin suggests, is the 

 same phenomenon as observed in Drosera, and must be attributed to 

 growth and not to injury as Darwin supposed. When flies are ar- 

 ranged along and more or less parallel to the leaf margin the growth 

 results in the rolling of it. There is Httle doubt of the correctness of 

 this explanation; and moreover it agrees with our knowledge of the 

 procedure in Drosera and Dionaea. 



Movement in Pinguicula is then an undoubted fact. How much sig- 

 nificance may be attached to it is a question. Goebel attached Kttle. 

 Darwin thought that the rolling of the leaf margin brings more glands 

 into contact with the prey, and in some cases pushes it into new posi- 

 tions further away from the margin. Darwin probably underesti- 

 mated the persistence of the change in movement, and therefore its 

 importance. The upward curved leaf margins help to hold the se- 

 cretion in place. This is probably as much as we can say about the 

 matter. 



Darwin then turned his attention to the question of secretion and 

 digestion. He found that when he placed prey (small flies), fragments 

 of meat, cartilage, fibrin, albumen (egg-white, coagulated), gluten and 

 gelatin, etc., on the leaf surface, there was an increase of secretion, 

 often copious, and that this was acid. Evidence of digestion was 

 clear: insects fell apart readily, and other substances showed the ex- 

 pected signs of disintegration. Objects not containing soluble nitrog- 

 enous matter, or other soluble matter do not excite secretion. Non- 

 nitrogenous fluids can cause free flow of the secretion, but this remains 

 neutral (non-acid). Among the substances or objects which incite 

 acid secretion were small leaves {Erica tetralix), pollen and various 

 seeds, all often seen to adhere to leaves in the open, aU, of course, con- 

 taining nitrogen from which Darwin argued that these objects also, as 

 well as animal prey, help to nourish the plant. Since the peduncles are 



