At the same time, such a case as this reveals again that mysterious and exquisite purposefulness which a reverent mind discovers in Nature everywhere. At the same time, as we have already pointed out, we are exceedingly ignorant of many of the very commonest facts. Léo Errera, the great Belgian botanist (whose recent death has been a terrible loss to science), collected together some facts as to the taste of cattle for various spiny and thorny plants; he found that cattle wished to eat the following: Buckthorn, whin or gorse, raspberry, brambles, the Scotch thistle, the creeping thistle, as well as musk, welted and slender thistles, sow thistle, and saltwort. They avoided: Barberry, the petty and German whin, rest harrow, the carline, and the other thistles not given above, as well as the common juniper. They disdained or despised: Sea holly, common holly, milk thistle, _Lactuca_, and _Urtica urens_.[95] [95] Errera, _Un Ordre de Recherches trop négligé_. See also Ludwig, _Biologie d. Pflanzen_, p. 210. So far as the holly is concerned, it is certainly not despised by sheep and rabbits in this country. But how few are the plants investigated! Several of the commonest British plants are omitted just because no one has taken the trouble to watch them. Here, then, is an opportunity of discovering something new, fresh, and interesting which should be well within the reach of any one who passes his life in the country. CHAPTER XV ON NETTLES, SENSITIVE PLANTS, ETC. Stinging nettles at home and abroad--The use of the nettle--Sham nettles--Sensitive plants--Mechanism--Plants alive, under chloroform and ether--Telegraph plant--Woodsorrel--Have plants nerves?--Electricity in the Polar regions--Plants under electric shocks--Currents of electricity in plants--The singing of trees to the electro-magnetic ear--Experiments--Electrocution of vegetables. The common nettle is one of our most interesting British plants. It is exposed to great danger; one sees it growing not only in pastures and parks, but in waste places, along roadsides, and near cultivated ground. Yet it is very seldom either eaten or even touched. Cattle do occasionally eat the young shoots. But this is exceptional, for even in fields where there are plenty of cattle great clumps of nettle luxuriate and increase in size every year.