474 FACTORS OF ORGANIC EVOLUTION. 



like. The varieties of cereals, which are old types, are so much alike 

 that expert knowledge is ueeded to distiDguish them. 



5. New types are more variable and flexible because less perfectly 

 molded into and adjusted to the circumstances of life than the old types 

 are. They have not yet reached the limits of their dissemination and 

 variation. They are generalized forms. 



The reader will please observe that I have here regarded the origin 

 and survival of the unlike in the plant creation in the sense of a plastic 

 material which is acted upon by every external stimulus, and which must 

 necessarily vary from the very force of its acquired power of growth, 

 and the unlikeuesses are preserved because they are unlike. I have no 

 sympathy with the too prevalent idea that all the attributes of plants 

 are direct adaptations, or that they are developed as mere protections 

 from environment and associates. There is a type of popular writings 

 which attempts to evolve many of the forms of plants as a mere protec- 

 tion from assumed enemies. Perhaps the plant features which have 

 been most abused in this manner are the spines, prickles, and the like, 

 and the presence of acrid or poisonous qualities. As a sample of this 

 type of writing, I will make an extract from Massee's Plant World: 



"Amongst the most prominent and general modes of protection of 

 vegetative parts against the attacks of living enemies may be mentioned 

 prickles, as in roses and brambles, which may either be straight, and 

 thus prevent the nibblings of animals, or, in more advanced species, 

 curved, thus enabling the weak stem to climb and carry its leaves out 

 of harm's way. Spines that are sharp-pointed abortive branches, serv- 

 ing the same purpose as prickles, as in the common sloe or blackthorn 

 {Primus spinosa). Eigid hairs on leaves and stem, as in the borage 

 [Borago officinalis) and comfrey (Symphytum officinale). Stinging hairs, 

 as in the common nettles ( Urtica clioica and tl. urens). In these cases 

 the stinging hairs are mixed on the leaves and stem with ordinary rigid 

 hairs, of which they are higher developments, distinguished by the lower 

 or basal swollen portion of the hair containing an irritating liquid that 

 is ejected when the tip of the hair is broken off. Bitter taste, often 

 accompanied by a strong scent, as in wormwood {Artemisia vulgaris), 

 chamomile {Anthemis nobilis), and the leaves and fruit of the walnut 

 {Juglans regia). Poisonous alkaloids, as in the species of Strychnos, 

 which contain two very poisonous alkaloids, strychnine and brucine, in 

 the root and the seeds; decoctions of species of Strychnos are used by 

 the Javanese and the natives of South America to poison their arrows. 

 Some of the species, as Strychnos nux vomica, are valuable medicines, 

 depending on the strychnine they contain, which acts as a powerful 

 excitant of the spinal cord and nerves; thus the most effective pro- 

 tective arrangements evolved by plants can be turned to account, and 

 consequently lead to the destruction of the individuals they were 

 designed to protect. Our common arum {Aru^ii maculatum), popularly 

 known as 'Lords and Ladies,' has an intensely acrid substance present 

 in the leaves, which eft'ectu ally protects it from the attacks of mammals 

 and caterpillars, but not from the attacks of parasitic fungi, which 

 appear to be indifferent to all protective contrivances exhibited by plants, 

 nearly every ])lant supporting one or more of these minute pests, the 

 effects of which will be realized by mentioning the potato disease, 

 'rust' and 'smut' in the various cereals, and the hop disease, all due 

 to parasitic fungi." 



