GROWTH BY THK ROOT. 11 



is conveyed from the earth into the plant, is the part 

 which is the soonest developed. Even in the embryo, 

 at the earliest commencement of germination, it is the 

 part immediately connected with the root that first 

 begins to move, by lengthening all its parts, and pro- 

 truding itself beyond the seed-coats into the earth. 



20. But as soon as this primitive lengthening of the 

 root has taken place, and the upper part of the embryo, 

 namely the young stem, has begun to exist as a sepa- 

 rate organ, the root changes its property, ceases to grow 

 by a general distension of its tissue, and simply in- 

 creases in length by the addition of new matter to its 

 point. A root is therefore extended much in the same 

 way as an icicle, by the constant superposition of 

 layer over layer to its youngest extremity ; with this 

 difference, however, that an icicle is augmented by 

 the addition of matter from without, while the root 

 lengthens by the perpetual creation of new matter 

 from within. 



21. For this reason, the extreme points of the roots 

 are exceedingly delicate, and are injured by very 

 trifling causes ; they, moreover, as all newly formed 

 vegetable matter is extremely hygrometrical, have 

 the power of absorbing, with rapidity, any fluid or 

 gaseous matter that may be presented to them. On 

 this account they are usually called spongekts. 



22. In the roots of ordinary Bxogens,* when the 



* [For an explanation of this term, see note under paragr. 60.] 



