164 MORPHOLOGICAL DEVELOPMENT. 



wise named, furnish conditions under which there is simi 

 larly an absence of determinate relations between the 

 parts of the flowers and the incident forces; and hence an 

 absence of bilateralness. This inconstancy of rela 



tive position is produced in various other ways by extreme 

 flexibility of the stems, as in the Blue-bell; by the ten 

 dency of the peduncles to curl to a greater or less extent 

 in diverse directions, as in Pyrola; by special twistings of 

 the peduncles, differing in degree in different individuals, 

 as in Convolvulus; by unusual laxity of the petals, as in 

 Ly thrum. Elsewhere the like general result arises from a 

 progressive change 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 symmetry 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 

 wards 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 

 233 T-J\ such as Petunia, or such as 

 Isoloma and Achimenes, 

 shown in Figs. 232 and 233. 

 j If these plants be examined, 

 it will be perceived that the 

 mode of growth makes the flower unfold in a partially one- 



