•>r 



26 THE BIOLOGY OF FLOWERING PLANTS 



very numerous but little branched ; whole system shallow. 

 Examples are Anemone nemorosa, Maianthemiim bifolium, 

 Paris qiiadrifolia. This type is characteristic of rich humus 

 soils. The rhizome replaces the roots as an anchoring 

 organ. (/) Adventitious roots of bulbous or corm plants 

 are numerous and more or less equal, with few or no branches 

 and few root hairs, e.g. Crocus, Hyacinthus, Scilla, Tulipa, 

 etc. {g) The adventitious roots are very numerous and 

 richly branched. This type approaches ((/), but there is 

 less distinction between the main roots and the laterals, 

 which are much more numerous. The majority of adven- 

 titious root systems probably belong to this type, which is 

 subject to much variation in the number and degree of 

 branching of the laterals ; examples are the sedges, grasses, 

 and cereals. Very long unbranched roots are produced, 

 among the others, by some cereals. In species growing in 

 sand, e.g. Carex arenaria, the branches are often extremely 

 fine, (h) The roots are strong and penetrate deeply without 

 branches (Orchis, Epipactis), with few branches (Hemero- 

 callis, Asparagus sps.), or with fairly numerous branches 

 (Helleborus). The roots are frequently fleshy and act as 

 storage organs. (/) The root system of aquatics may be 

 vigorous ; the laterals may be numerous but are generally 

 unbranched as in Ranunculus Flammula and Nymphsea ; fre- 

 quently there are no side roots, and in the case of submerged 

 plants the roots are often few and quite simple. Lemna 

 has a single root. 



As regards trees, a comparison between the root systems 

 of Picea exceha, Abies pectinata, and Pinus sylvestris was 

 made by Nobbe (1875). In the first year the pine has the 

 longest primary and much the largest number of secondaries 

 and tertiaries ; the fir is least branched. Later the side 

 roots of the pine dominate and form a veiy widespread 

 root system, while the primary continues in its growth 

 and forms a strong tap. The depth of the root system 

 and the relation of the tap to the laterals depend very 

 largely on the type of soil. The extent and plasticity of 

 the pine root system partly account for the success of the 





