Chap. XV. SECRETION. 335 



needle, tlie drop is generally withdrawn ; whereas with 

 Drosera there is no such difficulty, though the drops 

 are occasionally withdrawn. From this peculiarity, 

 when a small insect alights on a leaf of Drosophyllum, 

 the drops adhere to its wings, feet, or body, and are 

 drawn from the gland ; the insect then crawls onward 

 and other drops adhere to it ; so that at last, bathed 

 by the viscid secretion, it sinks down and dies, resting 

 on the small sessile glands with which the surface of 

 the leaf is thickly covered. In the case of Drosera, 

 an insect sticking to one or more of the exterior 

 glands is carried by their movement to -the centre of 

 the leaf; with Drosophyllum, this is effected by the 

 crawling of the insect, as from its wings being clogged 

 by the secretion it cannot fly away. 



There is another difference in function between the 

 glands of these two plants : we know that the glands 

 of Drosera secrete more copiously when properly 

 excited. But when minute particles of carbonate of 

 ammonia, drops of a solution of this salt or of the 

 nitrate of ammonia, saliva, small insects, bits of raw 

 or roast meat, albumen, fibrin or cartilage, as well as 

 inorganic particles, were placed on the glands of Dro- 

 sophyllum, the amount of secretion never appeared to 

 be in the least increased. As insects do not commonly 

 adhere to the taller glands, but withdraw the secretion, 

 we can see that there would be little use in their 

 having acquired the habit of secreting copiously when 

 stimulated ; whereas with Drosera this is of use, and 

 the habit has been acquired. Nevertheless, the glands 

 of Drosophyllum, without being stimulated, continu- 

 ally secrete, so as to replace the loss by evaporation. 

 Thus when a plant was placed under a small bell- 

 glass with its inner surface and support thoroughly 

 wetted, there was no loss by evaporation, and so much 



