THE SHAPES OF FLOWERS. 149 



ftbsence of determinate relations between the parts of the 

 floArV ers and the incident forces ; and hence an absence of 

 bilaterabiess. This inconstancy of rehitive position 



is produced in various other ways — by extreme flexibility of 

 the peduncles, as in the Blue-bell ; by the tendency of the 

 peduncles to curl to a greater or less extent in difierent 

 directions, as in Pyrola ; by special twisting of the peduncles, 

 difiering in degree in different individuals, as in Convol- 

 vulus; by extreme flexibility of the petals, as in Lythrum. 

 Elsewhere the like general result arises from a progressive 

 shange of attitude ; as in Myosotis, the stem of which as it 

 unfolds causes each flower to undergo a transition from an 

 upward position of the mouth to a lateral position ; or as in 

 most Cruciferce, where the like effect follows from an altered 

 direction of the peduncle. 



There are, however, certain seemingly anomalous cases 

 where radial sympathy is maintained by laterally-placed 

 flowers, which keep their parts in relative positions that are 

 tolerably constant. The explanation of these exceptions is 

 not manifest. It is only when we take into account certain 

 incident actions liable to be left unremembered, that we find 

 a probable solution. It will be most convenient to postpone 

 the consideration of these cases until we have reached the 

 general rule to which they are exceptions. 



§ 234. Transitions varying in degree from the radial to- 

 vv^ards the bilateral, are common in flowers that are borne at 

 the ends of branches or axes which are inclined in tolerably 

 constant ways. We may see this in sundry garden flowers 

 such as Petunia, or such as TydcBa and Achimenes shown in 

 ^^^ j^S3 ^A Figs. 232 and 233. If these 



^^ \yv^ plants be examined, it will 

 ^ , V " — O ) be perceived that the mode 

 vIX^j ( / \ V V of growth makes the flower 

 '^ — ^ unfold in a partially one- 

 sided position ; that its parts of attachment have rigidit}/ 



