13 



LECTURE II. 



of a plant thus arises from the embryonic root (radicle) : this is the oldest, grows most 

 vigorously, and penetrates deepest into the earth. It is, however, more frequently the 

 case, that the first root of the seedling, with its ramifications, soon ceases to grow, and 

 new, more vigorous roots are then formed from the lower parts of the shoot-axis, 

 which likewise, although they arise above the ground, penetrate into the earth 



and become branched there. 



^^IPJSlii ^^ ^"'^^ ^ cdiSt, more vigor- 



ous roots may go on con- 

 tinually appearing higher 

 up the stem, so that the 

 root - system ramifying in 

 the ground, arises, not as 

 before from a tap-root but 

 from the main stem of 

 the plant. The Palms and 

 the Maize furnish excel- 

 lent examples of this. In 

 creeping plants — e.g. the 

 Gourd — more especially 

 when the stem creeps for- 

 ward beneath the earth, 

 roots usually spring from 

 the under side of the shoot- 

 axis along its whole length, 

 in many cases even close 

 behind the bud, and these 

 may branch also in their 

 turn. In subterranean creep- 

 ing stems, the root- system 

 originally formed on the 

 seedling may then die off, 

 and rot away, together with 

 the hinder part of the stem 

 itself, new roots being con- ' 

 tinually produced behind 

 the apex of the growing bud. 

 But even when the primary 

 root-system remains pre- 

 served, but the stem climbs, 

 it frequently happens that 

 new roots are continually 

 produced below the bud; these then cling to solid bodies as climbing organs, as 

 m the Ivy and many tropical Aroids. Roots of this kind are commonly termed! 

 aerial roots ; they may also grow down from a considerable height in the form of thick, 

 cylmdncal cords several metres long, and finally penetrate into the ground, there to 

 become branched (tropical Aroids). But even in stems growing upright, it happens 



FIG 4 -Seedling of Gourd (Cucurbila Ptfo). w primary root; « secondary 

 (nat s'izel 'iyP°"'ty'='ionous segment of tlie slioot-axis i c the cotyledons 



