Chap. VI.] DIGESTION. 105 



decayed, and the edges of its cotyledons of a dark brown colour; 

 so that altogetlier live out of the seven seeds ultimately perished. 



Radish seeds (liaphanus sativus) 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 {Lepidium sativum) of the previous year were 

 placed on four leaves; two of these next morning were moderately 

 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 tena- 

 cious 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 of 3 hrs., and were still closely in- 

 flected on the third day; so that it evidently was not the mucus 

 which excited so much inflection; on the contrary, this served to 

 a certain extent as a protection to the seeds. Two of the six seeds 

 germinated whilst still lying on the leaves, but the seedlings, when 

 transferred to damp sand, soon died; of the other four se^s, only 

 one germinated. 



Two seeds of mustard {Sinapis nigra), two of celery {Apium 

 graveolens) both of the previous year, two seeds well soaked 

 of caraway (Carum carui), and two of wheat, did not excite 

 the leaves more than inorganic objects often do. Five seeds, hardly 

 ripe, of a buttercup (Ranunculus), and two fresh seeds of Anemone 

 nemorosa, induced only a little more effect. On the other hand, 

 four seeds, perhaps not quite ripe, of Carex sylvaUca caused the 

 leaves on which they were placed to be very strongly inflected; 

 and these only began to re-expand on the third day, one remaining 

 inflected for seven days. 



It follows from these few facts that different kinds of seeds 

 excite the leaves in very different degrees; whether this is solely 

 due to the nature of their coats is not clear. In the case of the 

 cress seeds, the partial removal of the layer of mucus hastened the 

 inflection of the tentacles. Whenever the leaves remain inflected 

 during several days over seeds, it is clear that they absorb some 

 matter from them. That the secretion penetrates their coats is also 

 evident from the large proportion of cabbage, radish, and cress 

 seeds which were killed, and from several of the seedlings being 

 greatly injured. This injury to the seeds and seedlings may, how- 

 ever, be due solely to the acid of the secretion, and not to any pro- 

 cess of digestion ; for Mr. Traherne Moggridge has shown that very 

 weak acids of the acetic series arc highly injurious to seeds. It 

 never occurred to me to obser>'e whether seeds are often blown on 

 to the viscid leaves of plants growing in a state of nature; but this 

 can hardly fail sometimes to occur, as we shall hereafter see in the 



