HOW PLANTS FLEE FROM THEIR ENEMIES. 4.3 



Wallace, in his work on Darwinism, says: 



" People do not see the constant and daily search after food, the failure to ob- 

 tain which means weakness or death ; the constant effort to escape enemies ; the ever- 

 recurring struggle against the forces of nature." 



This statement made with reference to animals, seems to apply- 

 equally well to plants. Again I quote from Wallace : 



"It is not so commonly known that if a garden is left to become altogether wild, 

 the weeds that first take possession of it, often covering the whole surface of the 

 ground with two or three different kinds, will themselves be supplanted by others, 

 so that in a few years many of the original flowers and of the earliest weeds may 

 alike have disappeared. This is one of the very simplest cases of the struggle for 

 existence, resultmg in the successive displacement of one set of species by another; 

 but the exact causes of this displacement are by no means of such a simple nature. 

 All the plants concerned may be perfectly hardy, all may grow freely from seed, yet 

 when left alone for a number of years, each set is in turn driven out by a succeeding 

 set." 



DeCandalle says: 



"AH the plants of a country are at war with each other, each one struggling to 

 occupy ground at the expense of its neighbor." 



Again from Wallace : 



" Besides this direct competition, there is one not less powerful arising from the 

 exposure of almost all plants "to destruction by animals. The buds are destroyed by 

 birds, the leaves by caterpillars, the seeds by weevils; some insects bore into the 

 trunk, others burrow in the twigs and leaves ; slugs devour the young seedlings and 

 the tender shoots, wireworms gnaw the roots. Herbivorous mammals devour many 

 species bodily, while some uproot and devour the buried tubers. 



" Besides having to protect themselves against competing plants and against 

 destructive animals, each species can sustain a certain amount of heat and cold, each 

 requires a certain amount of moisture at the right season, each wants a proper 

 amount of light or of direct sunshine, each needs certain elements in the soil. The 

 struggle for existence in plants is threefold in character and infinite in complexity. 



"We must not overlook the fact so well established that one of the greatest 

 points to be gained by migration, is to enable the flowers of different stocks of a 

 species to be cross-fertilized and thereby improved in vigor and productiveness. 



"No doubt many of these facts are familiar to you, if so, all the better, for we 

 can then discuss their meaning to greater advantage. They teach emphatically 

 some of the good reasons for a rotation of crops, which means new fields for old 

 or for new plants. As Lubbock says in his " Flowers, Fruits and Leaves" : 'Farmers 

 have found by experience that it is not desirable to grow the same crops in the same 

 field year after year, because the soil becomes more or less exhausted. The powers 

 of dispersion possessed by many seeds are a great advantage to the species. More- 

 over they are also advantageous in giving the seed a chance of germinating in new 

 localities suitable to the requirements of the species.'" 



People often think of animals as traveling from place to place, 

 but forget that plants can travel as well. By an almost infinite num- 

 ber of devices seeds and fruits of plants flee from the parental spot on 

 the wings of the wind, float on currents of ocean, lake and river. They 

 are shot by bursting pods and capsules in every direction. With hooks 

 and glands they cling to the coverings of animals. Allured by bril- 

 liant colors birds and many other animals seek and devour the fruits 

 of many plants, the seeds of which are preserved from harm by a solid 

 armor and are soon sown broadcast over the land ready to start 

 new colonies. Nuts are often carried by squirrels, a few in a place 

 for many rods and there securely buried. By a slow process which 

 amounts to considerable in a few years, many plants send forth roots, 



