ROOT SYSTEMS 27 



tree in diverse habitats. The fir is characterised by a 

 dominant tap and deep root system. The primary of 

 the spruce ceases growth after five years, and the root 

 system is entirely composed of shallow laterals. A spruce 

 uprooted by the v^ind is a common sight, and the shallowness 

 of its root system is then very evident. 



Broad-leaved trees have been investigated by Biisgen 

 (1905), who divides their root systems into two classes on a 

 different principle from Nobbe's. The ash has a system in 

 which the laterals are very long, moderately branched, and 

 with long terminal branches. The beech has a system in 

 which the laterals are not so long, but have very numerous 

 short and extremely fine terminals. The maples occupy 

 an intermediate position, and other trees show various 

 gradations. Of tropical trees investigated by Biisgen most — 

 such as the coffee and cinchona — belong to the ash type ; 

 the cocoa approaches the beech. Biisgen points out 

 that the ash type exploits a large volume of soil extetisively 

 and the beech type a smaller volume intensively. He 

 reaches the conclusion that the two are equally efficient as 

 water absorbers in different ways. 



From yet another point of view, Cannon (191 1) has 

 divided root systems into specialised and generalised. In the 

 former there is predominance of either a tap root or of the 

 laterals ; in the latter both tap and laterals are well developed. 

 The generalised systems are the more plastic, and plants 

 with such can occupy more varied habitats. 



Further Types o£ Root Systems and Their Extent. — Such 

 investigations yield information as to the plan of develop- 

 ment of root systems. We get indications, too, of the 

 depth to which a root penetrates or of the effectiveness 

 with which it exploits the soil. Many attempts have been 

 made to give a more exact account of the extent of various 

 root systems. The first of these occurs in one of the 

 earliest works on plant physiology, Stephen Hales' " Vege- 

 table Staticks " (1727) : "I dug up another Sun-flower, 

 nearly of the same size, which had eight main roots reaching 

 fifteen inches deep and sideways from the stem ; it had 



