6 BULLETIN OF THE NATURAL HISTORY SOCIETY. 



Of these, gravitation is of little importance since it can- 

 only effect movement downwards and not laterally. As 

 to the others, aside from the first which uses simply the 

 contractile power of protoplasni, some mechanical arrange- 

 ments must be provided so that the part may be brought 

 into contact with the moving power, and be moved by it. 

 This is in brief accomplished by the formation of new 

 individuals at the ends of runners, etc., in the second case, 

 by the drying or ripening of tissues under tension and 

 their sudden release in the third, by formation of wings or 

 plumes in the fourth, and of floats in the fifth, and finallj^ 

 by the development of hooks or stick}' coats, or of edible 

 fruits enclosing seeds protected from digestion, in the 

 sixth ; of course all kinds of combinations and gradations 

 between these methods occur. The principles of these 

 arrangements we must discuss in some detail. 



AVe must consider next what parts of plants can best 

 be locomoted. Excepting in the first and second, where 

 growth and locomotion go on together, it is necessary 

 that the part shall be capable of reproducing the organism 

 that it can hold its life for a time in suspension, that it 

 shall carry nourishment to give it a start in its growth, 

 and that preferably it shall be small and light. In some 

 cases, especially in the lowest cryptogamic water plants, 

 these qualities reside in the entire organism, and these- 

 move as a whole, but in the higher land plants there have 

 been developed special structures which combine these 

 qualities; these are in some cases, buds, in others spores, 

 and most important of all, seeds. Buds usually have the 

 disadvantage of not being able long to retain vitality 

 after separation from the parent plant, but seeds can 

 retain their life for much longer periods and during long 

 transportation, and it is in them that we find by far the 

 most perfect arrangements for locomotion. Indeed the- 



