350 ASSIMILATION. 



thrown back, bnt in the others its overarching is a conspicuous 

 feature. The mouth of the pitcher is strengtiiened by a thiclc 

 rim, near which are very numerous glands secreting a sweet 

 liquid. In the interior of the pitcher there is a conductive sur- 

 face, somewhat like that seen in Sarracenia. This extends for 

 some distance down from the mouth, and is frequently- crowned 

 by a sort of funnel-like appendage of the rim. Below the con- 

 ductive surface there is a secreting surface dotted with innu- 

 merable glands. According to Hooker, from whose notice many 

 of the facts here given are taken, there are three thousand of 

 these glands in a square inch. 



The fluid which collects in the pitchers has been shown by 

 Gorup-Besancz and Will to be neutral, or only verj' slightly- acid 

 in reaction, unless animal matter has been introduced. If, how- 

 ever, any animal matter has been placed in the pitchers, the 

 glands give forth an acid secretion, which contains an active 

 ferment that resembles pepsin and has the power of digesting 

 albuminous substances. It is an interesting fact that the neutral 

 secretion, although it has not the power of digesting albuminous 

 matters, becomes efficient at once upon the addition of a small 

 amount of acid (formic). During digestion the glands exhibit 

 the same phenomena of aggregation as observed in Drosera. 



The absorption of animal matter by Nepenthes has been 

 proved by the Lithium method. 



919. By the viscid or glandular hairs of a large number of 

 plants insects are sometimes caught, but to what extent these 

 hairs serve in digestion and absorption is not yet clear. From 

 experiments by Darwin, it appears that in some cases at least 

 thej' may aid the plant in absorbing ammonia compounds found 

 in rain and in the atmosphere, and that the glands may also 

 "obtain animal matter from the insects which are occasionally 

 entangled by the viscid secretion."^ One case merits particular 

 attention ; namely, that of 



920. Dipsacns, or Teasel. Francis Darwin has called atten- 

 tion to the extraordinary character of some of the hairs of this 

 plant. The following abstract gives onl}' the briefest outline 

 of his interesting paper. 



The glandular hairs arc multicellular and pear-shaped, being 

 supported by the small end on a cylindrical stalk, which rests on 

 an epidermal cell. At the summit of the gland where several of 



1 Darwin : Insectivorous Plants, p. 356. The oatchfly (Silene) should he 

 examined with reference to this point. 



