THE ABSORPTION OF WATER 



27 



irregular, in the first instance forcing their way to a moderate depth beneath the 

 surface of the soil, while the older roots rapidly fall behind in rate of develop- 

 ment. Again we meet with a third type where, while the earlier stages in 

 development are similar to those already described, the tap-root later on 

 surrenders its prominent position, then ceases to grow, and finally becomes 

 altogether abortive. To this type of root-system, found in trees more espe- 

 cially, we will recur again presently. In the fourth type the primary root 

 is wanting from a very early stage, and is replaced by a tuft of lateral roots, 

 equivalent in value, which arise from the base of the stem. Examples of 

 this type are furnished by grasses and bulbous plants. For descriptions of 

 the root-systems of herbaceous plants, a subject on which very little research 

 had hitherto been carried out, reference may be made to the comprehensive 

 work of Freidenfelt (1902). 



The root-systems of trees deserve special mention for two reasons ; first, 

 because these plants go on growing for many years, and because the enormous 

 amount of water used up by the crown of foliage imposes a specially heavy 

 demand on the activity of the root. Thanks to the elaborate researches of 

 NoBBE we are able to form a fairly good conception of the root-systems of 

 the pine, the fir, and the spruce. Nobbe (1875) cultivated seedlings of these 

 plants during one summer period in large glass vessels filled with sand, and, 

 when autumn arrived, estimated the number of roots and their collective 

 length after washing out the entire root-systems. Some of the data he ob- 

 tained are summarized in the subjoined table : — 



These three one-year-old plants, grown under exactly similar conditions, 

 exhibit highly striking differences, both in the number of their branch roots 

 and also in the total length of their root-systems. The sum of the lengths 

 of all the roots is, in round numbers, in the fir, im., in the spruce, 2m., in the 

 pine, 12 m. If estimated in surface measurement, we obtain areas of, in the 

 fir, 49-52 sq. mm., in the spruce, 64-33 sq. mm., and in the pine, 142-23 sq. mm. 

 Similarly, when the absorbing surface is considered, we find that the pine 

 again stands far ahead of the fir and the spruce. The mass of soil entangled in 

 the roots of the pine forms, according to Nobbe, a cone, 80-90 cm. in depth, 

 and with a surface area of 2,000 sq. cm. If we divide this cone into layers, 

 each 10 cm. in thickness, we find 1,548 lateral roots in the uppermost layer, 

 and, successively downwards, 217, 446, 366, 121, and 38 lateral roots. The 

 pine is thus in contact with a very considerable mass of soil by means of its 

 root-system ; thus it is able to put the soil to greater account, and so may succeed 

 in growing in what is otherwise an unfavourable situation. Its alleged in- 

 difference to its surroundings is thus shown to be due to its great power of 

 making the best of things. The behaviour of the plant in later years differs 

 very considerably from that of the seedling. A vigorous outgrowth of lateral 

 roots near the surface of the soil, in the case of the pine seedling, is suggestive 

 of the subsequent feebler power of growth on the part of the main root and 



