Funke — 81 — Photoperiodicity of Flowering 



Group IV [W-B] [R-D] 



Aethionema cappadocicum L Crambe hispanica L 



Aethionema diatrophis L Iheris amara L 



Aethionema grandiflorum L Iberis intermedia L 



Alyssum calycinum L Nasturtium silvestre L 



Anastatica hierochuntica L Neslea paniculata L 



Berteroa incana L Raphanus caudatiis L 



Brassica nigra L Raphanus salivus L 



Camelina sativa L Sinapis alba L 



Cheiranthus allionii S 5'i.sjim6Wit)ii sophia L 



Group II: [W-R-B] [D] : "red" and "blue" flower at the same time as 

 "white" ; the colour of the light is of no importance. Between groups I, II 

 and III all sorts of transitional cases occur. 



Group III : [W] [R-B-D] : flowering of long day plants only in "white" ; 

 neither red nor blue rays have any furthering effect ; vice versa for short day 

 plants. As R and B can act separately as darkness (groups I and IV), it is 

 theoretically possible that they can do so both at the same time ; neverthe- 

 less only 2 species belonging to this group have been found up till now. 



Group IV: [W-B] [R-D] : the opposite of group I; "blue" flowers at 

 the same time as "white," "red" at the same time as "dark." This group 

 seems to stand by itself ; all species which in my experiments were found to 

 belong to it are Cniciferae ; however, other members of this family belong 

 to groups 0, II or III. I think it remarkable that none of the Cruciferae 

 investigated so far belongs to group I, and the more so because otherwise 

 there is no indication of a relation between systematic position and photo- 

 periodical reaction. Indeed, it will be seen in the list that there are many 

 examples of genera whose species belong to different groups. 



Practically without exception it is to be stated that the photoperiod acts 

 differently on the reproduction and on the longitudinal growth. When e.g. 

 a long day species of group I is considered, the specimens in D and B re- 

 main vegetative, but those in D are always very short whilst in B the normal 

 length is reached. One of the few exceptions is presented by Campanula 

 rotundifolia. Therefore I think that an investigation into the influence of 

 photoperiod on auxin formation is urgently needed (20, 22) and could eluci- 

 date many obscurities in this field. 



This is especially the case for the phenomenon of reversibility induced 

 by photoperiod (9, 10, 12). Perilla ocymoides and P. ocymoides var. nanki- 

 nensis, especially nankinensis, are extreme types of short day plants belong- 

 ing to group II. In natural day length they remain vegetative till the end of 

 September. When the natural illumination is interrupted in May by a small 

 number of short photoperiods they blossom in the middle of the summer and 

 afterwards they show the reaction of reversibility, that is, the axes of the 

 inflorescences resume their vegetative growth ; towards the end of the sea- 

 son a second flowering stage follows. There seems to exist an equilibrium 

 between the formation of florigen during short days and of auxins during long 

 days. A large quantity of florigen, due to a great number of short photope- 

 riods, checks the formation of auxins with the consequence that after the first 

 flowering stage growth is not resumed and the life-cycle comes to an end. 

 Ocymoides is more sensitive in this respect than nankinensis ; in the former 

 7 short days determine the premature flowering, reversal and second flower- 



