CAP SELL A BURSA-PASTORIS. 237 



The primary root continues the plant axis below 

 the surface of the ground in the form of a tap root, and 

 thus enables the plant to take a deep and firm hold 

 upon the soil. Such primary roots are best developed 

 in dicotyledons and gymnosperms, remaining small in 

 monocotyledons and pteridophytes. 



The foliage, instead of being somewhat evenly dis- 

 tributed along the stem and its branches, is largely 

 collected at the surface of the ground in a cluster of 

 so-called root-leaves. The toothed and lobed outline 

 of the leaves with reticulated venation is quite charac- 

 teristic of dicotyledons. In Trillium (an anomalous 

 monocotyledon in this regard) there was presented the 

 palmate type of net-veined leaves, while in Capsella 

 we find the pinnate type, tending to narrower and 

 longer leaf forms. 



An exceptional feature of Capsella (and other 

 Cruciferce) is the entire suppression of bracts in the 

 flower cluster, giving the pedicels (branches) the 

 appearance of originating from the main axis without 

 subtending leaves. 



The structure of the flower is not typical of dicotyle- 

 dons, in which the type would be better expressed by 

 an arrangement like that of Trillium, after substituting 

 five for three as the type number. As a member of the 

 Cruciferce, however, Capsella has two whorls of two 

 sepals each, the lower (outer) being median (in the 

 plane of the axis) and the inner lateral ; one whorl of 

 four petals, alternating with the .four sepals ; two 

 whorls of stamens, the outer and shorter pair lateral, 

 the inner and longer set composed of four stamens, 

 arranged in axial pairs(tetradynamous) ; and one whorl 



