1642 A TEXTBOOK OF THEORETICAL BOTANY 



character of the hairs. In this way he separated two main groups, which 

 were further divided by the development of the style, and these groups 

 again were further separated on the number of nectaries, the shape of the 

 fruit and the character of the cells of the septum. Bayer based his classifica- 

 tion upon the distribution of the nectaries as the basic character while 

 Schweidler made use of the distribution of myrosin cells in the tissues in 

 his method of classification. 



Clearly no obvious system of subdivision can be adduced under the 

 circumstances and it is simply a matter of personal choice which set of 

 characters is regarded as most suitable for this purpose. While it is probably 

 true that Prantl's system makes use of the greatest number of characters and 

 might therefore be said to be the most natural, the system is unsatisfactory 

 because it employs as its foundation a character which modern research 

 has proved to be subject to change under environmental conditions. Hence 

 we can no longer regard the presence or absence of hairs as a diagnostic 

 character. There seems little to justify the preference of any one of the 

 other systems, and we shall therefore fall back on the original Linnaean 

 system, with the elaborations employed by Hooker. The following sum- 

 marizes these views so far as the British genera are concerned: 



I. Brassicoideae 



Pods elongated, dehiscing throughout their length, not compressed at 

 right angles to the septum. 



1. Arabideae. Flowers white, yellow or lilac. Seeds uniseriate, occa- 



sionally biseriate. Radicle accumbent. Matthiola, Cheiranthus, 

 Nasturtium, Barbarea, Arabis, Cardamine, Dentaria. 



2. Sisymbrieae. Flowers white, yellow or violet. Seeds usually uni- 



seriate. Radicle incumbent. Sisymbrium, Erysimum, Hesperis. 



3. Brassiceae. Flowers yellow. Seeds uniseriate or biseriate, radicle 



incumbent, longitudinally folded or very concave. Brassica, 

 Diplotaxis. 



II. Alyssinoideae 



Pods short, dehiscing throughout their length, not compressed at right 

 angles to the septum. Flowers white or yellow. 



1. Alysseae. Seeds biseriate, radicle accumbent. Draba, Erophila, 



Alyssum, Cochlearia. 



2. Camelineae. Seeds biseriate, radicle incumbent. Camelina, Subularia. 



III. Lepidinoideae 



Pods short, dehiscing throughout their length, much compressed at 

 right angles to the septum which is hence very narrow. 



I. Lepidieae. Cotyledons straight, incurved or longitudinally folded, 

 radicle incumbent. Flowers white. Capsella, Senebiera, Lepi- 

 dium. 



