218 



COMPENDIUM OF GENERAL BOTANY. 



are in the same horizontal plane, "verticillate." Example: the 

 Isiliiflorce. 



2. Acyclic flowers: spiral arrangement of the floral leaves. 

 Example : Magnolia. 



3. Ilemicydic flowers : the floral organs may in part be spirally 

 arranged (especially the calyx) and in part verticillate. Example : 

 JRanunculacece. 



The calyx usually forms one circle of floral leaves; the corolla 

 also one ; the androecium one or two ; the gyncecium usually one. 

 For causes more or less associated with the mechan- 

 ical theory of phyllotaxy there is often noticeable 

 an alternate arrangement of members of the vari- 

 ous verticillse, provided they occur in equal num- 

 bers (see Fig. 139). The whorls or verticillae may 

 also be opposite, as shown in Fig. 140. 



A further discussion of these relations would 

 soon lead us to that stage of investigation in which 

 the comparative morphology of flowers seems to 

 give evidence of the transmutation of one genus into another. 

 We will cite an example. Normally the Scrofulariacece have five 

 stamens; Veronica has two; Gratiola has two 

 normal stamens and two sterile structures, the so- 

 called ' ' staminodia. ' ' Digitalis and Scrofidaria 

 have four stamens and one staminodium. It is 

 evident that the abortion or the suppression of stamens 

 plays an important part in the cases mentioned. By 



FIG. 139. Dia- 

 gram of the 

 flower of Lili- 



Krass and 

 Landois.) 



this ' ' suppression ' ' 



FIG. 140. Dia- 

 gram of the 

 is meant the non-appearance of flowerofPnw- 



an organ which one would expect to appear accord- (A Jjf*' Krass and 

 ing to reasons deduced from comparative morphology. Landois.) 

 In some cases an entire whorl may be suppressed or fail to appear. 

 In other cases there is not a suppression of members, but an increase 

 in the normal number of parts (" dedoublement "). 



Since SCHUMANN' has applied SCHWENDENER'S contact theory to 

 the processes of growth and development in the floral region of 

 the plant the investigations in regard to this subject have been 

 placed upon a firmer foundation, while the play of fancy is to a cer- 

 tain extent checked. The exact history of development, the study 



1 Neue Untersuchungen liber den Bltiteuanschluss, Leipzig, Engelmann, 1890. 



