SPACE OCCUPIED BY ROOTS. 



13 



frequently enough that roots arise immediately beneath the growing point, and even 

 that the whole root-system of the plant consists of them, as occurs in many Ferns, 

 particularly the Marattiacese and many tree ferns. In several species of Cactus, 

 moreover, the tendency also exists to put forth roots close beneath the growing 

 point of the shoot; finally, roots may even spring out of leaves, as occasionally 

 happens in a fortuitous manner, but occurs 

 quite normally in our common large Fern, 

 Aspidium Filix-mas, where the shoot-axis is 

 so densely beset with leaves, that it generally 

 shows no proper surface at all ; all the 

 numerous roots of this plant spring from 

 the basal parts of the leaves. 



Since the roots developed in the earth 

 especially absorb water and nutritive matters 

 dissolved in it, their number and ramifica- 

 tions, and thus the whole formation of the 

 root-system, are the richer, the more vigor- 

 ously the green, transpiring and assimilat- 

 ing leaf-surface of the aerial shoots is de- 

 veloped. In time, in proportion as the 

 assimilating foliage increases in surface, the 

 subterranean root- system becomes larger, 

 and fresh portions of the soil are pene- 

 trated by it. The number of root-fibres, 

 and the space which they traverse in all 

 directions within the soil, is much larger 

 than one usually supposes. It is cer- 

 tainly not put too high if we assume this 

 space to be more than a cubic metre in 

 the case of a well-developed Sunflower, 

 Hemp, or Gourd plant; and in the case 

 of large trees we may estimate it even 

 at hundreds of cubic metres. This space 

 then is so traversed in all directions by 

 thousands of fine roots, that scarcely a 

 cubic centimetre of it remains exempt. By 

 this means the plant," abundantly provided 

 with foliage, succeeds in extracting from 

 the soil the very large quantities of water 

 which are transpired from the leaves, to- 

 gether with the nutritious matters contained 

 in it. S. Clark has taken the trouble to 



measure the length of all the roots of a large Gourd ])lant, and found that 

 it amounted to twenty-five kilometres. This relation between root-formation 

 and leaf-surface makes itself evident again in that, in floating aquatic plants 

 {Hydrochari's, Siratiotes, Lemnd). the number and lcn,L;lh of the roots are 



Fig. 5.— Diagrammatic longitudinal section through a yoims 

 Maize plant (Zea Mays), lu primary root ; ^ <j)' ((,'", the 

 roots springing from the shoot axis (.r) ; * leaves ; i buds. 

 The growing points are represented black, the elongating parts 

 grey ; tlie portions left white arc fully grown. 



