THE WHITE LILY 173 



the stem of the seedling is perhaps an eighth of an 

 inch thick. In the Palms the difference is much more 

 striking ; the thin stem of the seedling, only a small 

 fraction of an inch in thickness, may give rise to a 

 great trunk, two feet or more in diameter, and yet 

 there is no cambium and no formation of secondary 

 tissues. How is this possible ? The explanation is 

 that the thin stem of the seedling never does become 

 any thicker, but for a time the vigour of the growing 

 point constantly increases, so that each node and 

 internode which is added to the stem is thicker than 

 the last. Thus for a time the stem has the form 

 of a cone standing on its apex. But sooner or later 

 the growing-point reaches its full strength. From 

 this time onwards the portions of the stem which it 

 successively produces are of equal diameter ; thus all 

 the upper part of the stem is cylindrical. The older 

 part of the stem, which alone has the form of an 

 inverted cone, generally becomes buried in the ground, 

 or like the tap-root it may die away altogether. 



In typical Monocotyledons, then, the increasing 

 diameter of the stem is due to the addition of suc- 

 cessively thicker nodes and internodes, and not to 

 the growth in thickness of those already formed. 



III. INTERNAL STRUCTURE AND DEVELOPMENT 

 OF THE REPRODUCTIVE ORGANS 



The flower of a Lily is not only very favourable for 

 study, from the large size and simple arrangement of 

 all its parts, but it has the more important advantage 



