18 MORPHOLOGY OF ANGIOSPERMS 



members appear in acropetal succession along a continuous low 

 spiral, and just when one set of members stops and the next 

 begins is indefinite within certain usual limits. There seems 

 no doubt in this case that the primordia are indifferent up to 

 a certain stage of development, and that the particular organ 

 produced depends upon something outside of the essential con- 

 stitution of the primordium itself. In the case of cyclic flowers, 

 in which toral growth in length has been checked and there has 

 been growth in diameter, the acropetal succession of members 

 is often very much interfered with. The " disturbances " that 

 arise in the torus by substituting growth in diameter for growth 

 in length account not only for the breaking up of the acropetal 

 succession, but also for the inequality of members of the same 

 cycle, or of different regions of the cycle. It is evident that in 

 the case of cyclic flowers organogeny must 'deal 'not only with 

 the succession of cycles, but also with the succession of mem- 

 bers in each cycle. Definite data in reference to these points 

 are not so available as they should be, but a few illustrations 

 may be cited. 



For the majority of cyclic 'flowers it seems to be assumed 

 that the cycles appear in acropetal succession namely, sepals, 

 petals, stamens, carpels and that the members of each cycle are 

 practically synchronous in origin, but it is probable that this 

 assumption is gratuitous. While theoretically it may be as- 

 sumed that the cycles should arise in acropetal succession, the 

 fact that they do not in many observed cases indicates that 

 they may not in many more cases ; and the synchronous ap- 

 pearance of the members of a single cycle is unsound as a 

 theoretical assumption. Hofmeister * records that in Rosa, 

 Potentilla, and Rubus the primordia of the carpels appear be- 

 fore those of the stamens have reached the full number, and 

 that in Hypericum calycinum the primordia of the sepals ap- 

 pear after those of the stamens. It is also generally known 

 that among the Compositae (Fig. 3), D^psaceae, Valerianaceae, 

 and Rubiaceae, in which the sepals are much reduced or modi- 

 fied, their primordia do not appear until after those of the 

 stamens and carpels; and that among the Cruciferae (in Cap- 

 sella, at least) (Fig. 4) the petals are the last members to 



* HOFMEISTER, W. Allgemeine Morphologic der Gewachse. Leipzig. 1868. 

 p. 462. 



