CRUCIFER.E. 



181 



193). Two are anteroposterior (or placentary) ; they have flat bases 

 inserted along a very open arc ; in the bud they cover the lateral (or 

 carpellary) pair. These are dilated and boat-shaped at the base ; 

 and the scar of their insertion on the receptacle is much curved. 



Cheiranthus Cheiri. 



Fig. 198. 

 Seed. 



Fig. 199. 

 Transverse section of seed (|). 



Fig. 200. 

 Embryo (*). 



There are four alternipetalous petals, forming a cruciform corolla. 

 Each one (fig. 193) consists of a long narrow claw, and a much 

 broader blade, which is inclined to the claw. The prsefloration is 

 somewhat variably imbricated ; as a rule one petal is wholly external, 

 one wholly internal, and the two others are covered on one edge and 

 overlapping on the other (fig. 193). The androceum is tetradyna- 

 mous ; i.e., of its six stamens four are larger than the remaining two. 

 The latter are superposed to the lateral sepals, the four large onos 

 are superposed in pairs to the antero-posterior two. 1 Around the 

 foot of the stamens the receptacle swells into a green glandular 

 tissue, constituting what have been termed the nectaries, or disks. 

 In this species they form two large irregular islands, surrounding 

 the feet of the short stamens (fig. 193). Each stamen (fig. 196) has 

 a free subulate filament, and an introrse two-celled anther of 

 longitudinal dehiscence. 2 The gynaeceum is superior ; it has a sub- 

 sessile narrow elongated subcylindrical ovary, surmounted by a short 

 style, whose apex is divided into two little lateral diverging lobes, 

 covered on their inner faces with stigmatic papillae. The ovary 

 is one -celled, with two antero-posterior parietal placentas. Each 

 bears two series of funiculate descending campylotropous ovules, 

 whose micropyles look upwards and inwards ; 3 and between its series 



1 Certain authors hold that these are epposi- 

 tipetalous, and form a distinct whorl to the lateral 

 stamens. 



- The pollen of Cruel/era is generally formed 

 of opaque ovoid grains, with three iolds. H. 

 Mohl (in Ann. Sc. Nat., ser. 2, iii. 327) dis- 

 tinguishes those with a cellular and with a dotted 



external membrane. In the former the bands 

 are smooth {Raphamis Raphanistrum, Sinapis 

 arvensis, Cardamine pralensis), or cellular (Chei- 

 ranthus annaus, various species of Iberis). In 

 Cheiranthus incanus and tr>cuspidatus there are 

 no folds. 



3 They have two coats. 



