Ways in Which Plants Increase in Size 



339 



ripening fruits to a safer position under water. But an actual 

 shortening occurs in the roots of some herbaceous perennials, 

 like the Dandelion, which thus are enabled to keep their stems 

 safely underground despite a certain annual increase in length. 



FIG. 127. A stem 

 of Melothria, just 

 marked by 

 evenly- spaced 

 cross marks, and 

 the same stem a 

 day or two later. 



The same thing is said to occur in the lateral rootlets of some 

 bulb-bearing plants, like the Tulips, with this marked advantage, 

 that the newly formed bulblets are drawn clear of the old parent 

 bulb. Mechanically, this shortening is variously effected, but 

 chiefly by a forcible lateral expansion of the tissues, somewhat on 

 the principle by which a muscle is shortened; and as a result 

 such roots commonly show a number of transverse wrinkles. 



