REPRODUCTION OF PLANTS. 99 



division ; and this is either natural or artificial, 

 and depends on two circumstances : in one, the 

 ascending organs are first developed, or in other 

 words an adventitious leaf bud (35) is produced, 

 and these favour the subsequent development 

 of the roots ; in the other, roots are first formed, 

 and by their action promote the development of 

 the ascending system. The former is in gene- 

 ral the case when the germ is found surrounded 

 by a sufficient deposit of nourishment to sustain 

 it till it can push forth its roots : this nourish- 

 ment is furnished by the mother plant from the 

 descending juices. To this sort of buds may be 

 given the general name of tubercles, though bo- 

 tanists designate them by a variety of appella- 

 tions. In all tubercles a phenomenon occurs 

 which distinguishes their germination from that 

 of seed ; in the latter the radicle is always first 

 developed, while in the tubercle the ascending 

 part, that which corresponds to the plumule, 

 is first put forth. The common potato is an 

 instance of this mode of increase ; the tubercles 

 are detached towards the end of the year either 

 by the death of the stem on which they grow, 

 or by the slightest accident, and falling on tin- 

 ground, vegetation ensues. This single exam- 

 ple is sufficient for the present purpose ; the 



