102 



HUTCHINSON'S POPULAR BOTANY 



it is reckoned that no less than 500,000,000 pounds of nitrogen are thus 

 obtained from the air annually by this method of cropping in that 

 country. 



Marshy places are usually very deficient in certain of the nutrient 

 elements, as nitrogen, potash, and other salts, and plants which grow in such 

 neighbourhoods, being often hard put to it to obtain a sufficiency of food, 



take to crime for a liveli- 

 hood. Finding, we know 

 not how, that gnats and 

 flies and other species of 

 the great class of Insects 

 contain in their bodies the 

 aliment which is so deficient 

 in the soil, the plants actu- 

 ally prepare traps for the 

 capture of these winged 

 creatures, which they kill 

 and eat without compunc- 

 tion. 



Many have found a 

 difficulty in receiving the 

 statement ; nor is a little 

 scepticism surprising. One 

 such plant is the little 

 Round-leaved Sundew 

 (Drosera rotundifolia, fig. 

 130), whose round leaf- 

 blade bears about a couple 

 of hundred red tentacles, 

 each ending in a globular 

 head from which a clear 

 drop of gum exudes and 

 glistens like a drop of 

 dew. These sticky glands 

 close round the insect 

 prisoners, and these move- 

 ments are accompanied by 

 the excretion of a digestive ferment comparable with animal pepsin, which 

 dissolves all the nitrogenous constituents of the victim, just as the gastric 

 juice of our bodies would dissolve an oyster. 



There are three British species of Sundew, all of which are insecti- 

 vorous. The round-leaved (Drosera rotundifulia) is perhaps the prettiest, and 

 it is to be met with in many places growing amid wet Sphagnum Moss. 

 Equally plentiful is the Intermediate Sundew (Drosera intermedia), with 



FIG. 136. MEXICAN BUTTEBWOBT (Pinguicula caudata). 



The Butterworts catcli small insects by means of a viscid secretion from 

 the glands of the leaves. One of these glands, viewed sideways and 

 enlarged, is shown above. The other figure shows the head of the gland. 



