INTERDEPEXDEXCE OF ORGANISMS 



13 



hedged about with spines or glandular hairs, or hidden 

 at the bottom of deep or closed passageways — and thus 

 reserved for the use of proper guests. 



c) The floral organs may become grown together 

 in various ways. This tendency toward fusion of 

 parts is strongest among the pistils and the petals. In the 

 loosestrife flower (fig. 3) all the petals and stamens are 

 grown together at the base. This stiffens the flower, and 

 makes it better able to support the trampling of a visiting 



insect. Often the fu- 

 sion of parts is of great 

 importance in se- 

 questering nectar (fig. 

 21) and forming the 

 passageways thereto. 

 This is the meaning of 

 the various forms of 

 corollas, the principal 

 types of which are 

 shown in the accom- 

 panying diagram (fig. 7). 



d) The parts may become unlike in each whorl, making 

 the flowers irregular: or 



e) They may lose their symmetrical arrangement, and no 

 longer alternate regularly in each whorl: or, 



f) Some of the parts may be lost through atrophy: or 



g) The flower may cease to be radial and become bilateral. 

 This point is the concomitant of the three preceding. Bi- 

 lateral flowers show the completest structural adaptations 

 to insect visitors. They generally face laterally, and are so 

 shaped that the insect enters in one position only. The 

 corolla is usually two-lipped, with the lower lip serving as an 

 alighting place, and the upper as a shelter for the pollen 

 (fig. 8). The stamens are often reduced to one or two pairs, 



Fig. 8. Typical bilabiate flowers of Prunella 

 (P. vulgaris L.) 



