INTRODUCTION 37 



for germination and the resistance of the seed to 

 cold in different species may afford interesting results. 



When the early stages of germination are con- 

 cluded the plant is marked out into definite regions 

 of root, stem, and leaves ; and later the flower 

 develops, to be followed by the fruit. 



The root and its rootlets adapt themselves to the 

 character of the surroundings, and in these various 

 ways and means of adjusting their organs to meet 

 certain conditions there are many interesting prin- 

 ciples involved. The way in which the root serves 

 its purpose of acting as an organ of attachment 

 affords scope for interesting observations. It will 

 vary in wet and in dry situations. Aquatic plants 

 differ markedly from land plants in this respect. 

 The modifications required in the case of crevice 

 plants and those plants that live on walls in the 

 crevices of stones or bricks may be contrasted with 

 the roots of such plants as parasites on grasses, etc., 

 or saprophytes. The tubercles developed on Legu- 

 minosae and other plants such as the Alder, which 

 have bacteria in them, and the relation of these 

 to the soil and the plant, are interesting from 

 the economic standpoint. The study of the modifi- 

 cations in the roots of some wild plants cultivated 

 as vegetables is also of the same value. 



The relationship of the root to the water in the 

 soil, to the salts in solution, and air in the soil, and 

 the utilisation of all these factors in its life-history 

 forms part of the natural history of the plant. 



