IV] THE FLOWER AND METAMORPHOSIS 51 



over the stem of the leafy shoot may be continued 

 directly upwards into the flower. Here, however, it 

 abruptly terminates, while in the leafy shoot it may 

 continue to grow indefinitely at the tip. The result 

 of this is that the flower is borne at the end of its 

 stalk. The relation of the appendages or leaves to 

 this stem is similar in the foliage-shoot and the 

 flower. In either case they arise laterally upon it, 

 and their succession is such that the oldest are 

 lowest down, and the youngest nearest to the tip. 

 In many cases the appendages are developed equally 

 all round the stem, giving what is called a radial form 

 to the shoot or flower, and this is believed to be 

 a relatively primitive condition. But both foliage- 

 shoots and flowers may be unequally developed, the 

 appendages growing stronger on one side than on the 

 other. This results in lopsided forms, and it can often 

 be shown that their lopsidedness originated as an 

 adaptation to meet special needs of the organism: 

 in fact it is regarded as a secondary modification in 

 the history of descent. The flowers of a Pea or an 

 Orchid will serve as illustrations of this. In these 

 cases the adaptation has been to fit them for the 

 insect visits which are essential for the process of 

 cross- pollination. Lastly, the parts of the flower are 

 as a rule closely aggregated together, Avhile those of 

 the vegetative shoot may commonly be separated by 

 intervals of the elongated stem. But all the leafy 



4—2 



I 



