8o ASSOCIATION OF ORGANISMS THE WEB OF LIFE 



tracted, by means of an anti-toxin extracted from the blood of 

 the horse. 



Turning to the other side of the question, we find that 

 numerous plants are protected by various means against vege- 

 tarian animals. Many species, for example, more or less suc- 

 cessfully ward off the attacks of browsing forms by mechanical 

 devices. Of this nature are the thorns, spines, prickles, and 

 stinging hairs with which painful experience has made most of 

 us more or less familiar. Good illustrative cases are such com- 

 mon forms as gorse, blackthorn, holly, thistle, and stinging-nettle. 

 This is not, however, the only use of sharp-pointed outgrowths, 

 for not a few forms, e.g. the bramble, are "hook-climbers". It 

 is particularly noticeable that ripening fruits are often mechani- 

 cally guarded, the prickly husks of horse- 

 chestnut being a case in point. 



Quite a number of herbaceous plants 

 contain in their soft tissues bundles of 

 exceedingly sharp needle - like crystals 



Fig. 1075. Cell from Leaf of Vir- / i . -, r \ 1 i 1 



ginia Creeper (Ampelopsis], containing (raphldCS, tig. IO75) Which prOtCCt them 



against the ravages of slugs and snails, 

 as experiment has shown. Many such 



crystals are to be found, for example, in the leaf-stalks of the 

 Arum- "Lily" (Richardia sEthiopica). 



Many plants are protected by chemical means, i.e. by the 

 formation within their tissues of substances which are poisonous 

 or nauseous, or otherwise detrimental to the well-being of would- 

 be consumers. Forms such as Foxglove, Aconite, Monkshood, 

 Hemlock, and Yew no doubt ward off to a great extent the 

 attacks of browsing animals in this way. Fruits and seeds 

 are often thus protected, and may be either simply nauseous 

 (especially when unripe) or else contain active poisons, as in the 

 case of the seeds of Laburnum and Strychnos nux-vomica. The 

 attacks of both large and small animals are checked in many 

 cases by means of a sticky fluid known as latex, which flows 

 from an injured part, and when fresh has a milky appearance. 

 Common examples among British plants are the Spurges 

 (Euphorbia), Poppy, Greater Celandine, and Dandelion. This 

 secretion hardens when dry, and forms a protective coat over the 

 wound. Some tropical trees produce a kind of latex which, in the 

 solidified condition, is known to us as india-rubber. It is almost 



