86 BRITISH FLOWERING PLANTS chap. 



SUBULARIA 



S. aquatica (Awlwort). — This is a small aquatic 

 plant generally not more than two, seldom three, inches 

 high. It usually grows entirely under water, and the 

 flowers are cleistogamous. Sometimes, however, it is 

 aerial, in which case the flowers open. The anthers 

 and stigma ripen simultaneously and are closed together. 

 Scott Elliot, in Dumfriesshire, observed a fly on the 

 flower, and this appears to be the only insect visitor on 

 record. It is named from subula, an awl, from the 

 shape of the leaves, a form recurring in other submerged 

 herbs, as, for instance, in the Quill wort (Isoetes). 



Senebiera 



S. didyma. — The silicule or fruit is so much con- 

 stricted as to be almost two-lobed, whence the specific 

 name from the Greek StSuyuo?, twin. It is reniform, much 

 compressed laterally, notched, and deeply and irregularly 

 pitted, ultimately separating into two indehiscent pieces, 

 each containing a solitary seed conforming rather closely 

 to the cavity. The seed is reniform, laterally compressed 

 and rugulose, with longitudinal furrows corresponding to 

 the outline of the folded cotyledons and radicle. The 

 coat is pale yellow, thin, somewhat transparent, and 

 densely and finely rugulose. The notch at the base of 

 the fruit favours its temporary attachment to passing 

 animals, and in this way the seeds may often be carried 

 from the parent plant. The species is a native of 

 temperate South America, but has been introduced into 

 many countries. It is well established on the sea-coast 

 of Hampshire, South and West Wales, South and West 

 Ireland, and appears sporadically elsewhere. 



Thlaspi (Penny Cress) 



The name is derived from the shape of the pods. 



T. alpestre. — There are not a few plants in which the 

 petals change colour, but this does not often happen in 

 the case of the anthers. Those of this species, however, 



