ROOT SYSTEMS 25 



The root systems of different plants thus come to differ 

 both in plan and in extent, and these differences are largely 

 specific, though the type shown by any species, and more 

 particularly its extent, may be influenced by external condi- 

 tions. As the success of a plant may be determined by the 

 suitability of its root system to exploit the particular soil 

 conditions of the habitat, certain habitats are associated with 

 plants of particular root types. 



Types of Root System. — ^The roots of herbaceous 

 plants have been studied by Freidenfeldt (1902) in relation 

 to the plan of their systems. He distinguishes and classifies 

 thirteen types with various sub-types. These do not all seem 

 to be very well marked, nor is the classification satisfactory, 

 but a description of the most distinctive gives an idea of the 

 variety to be met with. 



1 . Main root types : 



{a) The primary root does not persist and is soon 

 replaced by a strongly developed system of laterals, typically 

 shallow rooting ; characteristic of weeds of cultivated soil 

 or fertile waste ground. Examples are Galeopsis Tetrahtt, 

 Veronica agrestis, Chenopodium album, Stellaria media, 

 (b) Deep systems with a permanent and persistent primary 

 root and few laterals ; shown by annuals such as Reseda 

 Luteola, Plantago Coronopus, and perennials such as Plantago 

 media, Taraxacum officinale. In most biennials and some 

 perennials the tap root forms a fleshy store, e.g. carrot, 

 parsnip, (c) Intermediate between (a) and {b) with a 

 persistent and well-developed primary and also well- 

 developed laterals, e.g. pea, Atriplex sps., Polygonum 

 aviculare. 



2. Adventitious root types : 



(d) A number of strong descending adventitious roots 

 with sharply differentiated, smaller absorption roots, 

 each resembling a system of type (<:). Examples are the 

 nettle, primrose, Plantago lanceolata, and Plantago major, 

 {e) Adventitious roots produced on long rhizomes, fine, 



