CHAP. VI. DIGESTION. 127 



and we know that leaves immersed in an emulsion of starch 

 are not at all affected. I need hardly say that starch is not 

 digested by the gastric juice of animals. 



Action of the Secretion on Living Seeds. 



The results of some experiments on living seeds, selected by 

 hazard, may here be given, though they bear only indirectly on 

 our present subject of digestion. 



Seven cabbage seeds of the previous year were placed on the 

 same number of leaves. Some of these leaves were moderately, 

 but the greater number only slightly inflected, and most of 

 them re-expanded on the third day. One, however, remained 

 clasped till the fourth, and another till the fifth day. These 

 leaves therefore were excited somewhat more by the seeds than 

 by inorganic objects of the same size. After they re-expanded, 

 the seeds were placed under favourable conditions on damp 

 sand ; other seeds of the same lot being tried at the same time 

 in the same manner, and found to germinate well. Of the seven 

 seeds which had been exposed to the secretion, only three ger- 

 minated ; and one of the three seedlings soon perished, the tip 

 of its radicle being from the first decayed, and the edges of 

 its cotyledons of a dark brown colour; so that altogether five 

 out of the seven seeds ultimately perished. 



Eadish seeds (Raplianus sativuii) of the previous year were 

 placed on three leaves, which became moderately inflected, and 

 re-expanded on the third or fourth day. Two of these seeds 

 were transferred to damp sand ; only one germinated, and that 

 very slowly. This seedling had an extremely short, crooked, 

 diseased, radicle, with no absorbent hairs ; and the cotyledons 

 were oddly mottled with purple, with the edges blackened and 

 partly withered. 



Cress seeds (Lepidum sativnm') of the previous year were 

 placed on four leaves ; two of these next morning were mode- 

 rately and two strongly inflected, and remained so for four, 

 five, and even six days. Soon after these seeds were placed on 

 the leaves and had become damp, they secreted in the usual 

 manner a layer of tenacious mucus; and to ascertain whether 

 it was the absorption of this substance by the glands which 

 caused so much inflection, two seeds were put into water, and 

 as much of the mucus as possible scraped off. They were then 

 placed on leaves, which became very strongly inflected in the 

 course ot 3 hrs., and were still closely inflected on the third 

 day ; so that it evidently was not the mucus which excited so 



