CHAP. VI. DIGESTION. 103 



were completely liquefied; two others were rendered 

 transparent, but not quite liquefied; whilst the fifth 

 was but little affected. Several glands on the three 

 latter leaves were now moistened with a little saliva, 

 which soon caused much inflection and secretion, 

 with the result that in the course of 12 additional 

 hrs. one leaf alone showed a remnant of undigested 

 tissue. On the discs of the four other leaves (to one 

 of which a rather large bit had been given) nothing 

 was left except some transparent viscid fluid. I may 

 add that some of this tissue included points of black 

 pigment, and these were not at all affected. As a 

 control experiment, small portions of this tissue were 

 left in water and on wet moss for the same length of 

 time, and remained white and opaque. From these 

 facts it is clear that areolar tissue is easily and 

 quickly digested by the secretion ; but that it does 

 not greatly excite the leaves. 



Cartilage. Three cubes ( T V of an inch or 1'27 mm.) 

 of white, translucent, extremely tough cartilage were 

 cut from the end of a slightly roasted leg-bone of a 

 sheep. These were placed on three leaves, borne by 

 poor, small plants in my greenhouse during Novem- 

 ber ; and it seemed in the highest degree improbable 

 that so hard a substance would be digested under 

 such unfavourable circumstances. Nevertheless, after 

 48 hrs., the cubes were largely dissolved and con- 

 verted into minute spheres, surrounded by trans- 

 parent, very acid fluid. Two of these spheres were 

 completely softened to their centres ; whilst the third 

 still contained a very small irregularly shaped core 

 of solid cartilage. Their surfaces were seen under 

 the microscope to be curiously marked by prominent 

 ridges, showing that the cartilage had been un- 

 equally corroded by the secretion. I need hardly 

 8 



