CHAPTER XV. THE SPERMAPHYTA. 379 



with it, and are enfolded by it. As this is the only conspicuous 

 one, it is called the cotyledon. The embryo is usually straight 

 and cylindrical or obconical, from the thickening of the cotyle- 

 don toward its upper end, but in a few cases, as in Potomogeton, 

 it is elongated and coiled. The axial part (caulicle and radicle) 

 is usually very short and nearly enclosed in the relatively large 

 cotyledon, but in Sagittaria, Vallisneria, Hydrocharis, and their 

 relatives, the axis is more conspicuous than the cotyledon. 

 When the seed germinates, in some cases the radicle scarcely 

 grows at all, but is almost immediately displaced functionally by 

 adventitious roots which spring from above it, as in the Grasses ; 

 but in most cases it grows vigorously for a short time and then 

 stops, giving way to adventitious roots. 



The sub-class includes about fifty natural orders, and upwards 

 of eighteen thousand species, which are distributed into seven 

 sub-divisions, as follows : 



Division A. — The Helobice. 



Division B. — The Glumiflorce. 



Division C. — The Sbadicifloroe or Nudiflorce. 



Division D. — The Enantioblastce. 



Division E. — The Scitaminece. 



Division F. — The Gynandrce, and 



Division G. — Liliiflorce. 



The Helobiae are all marsh or water plants, some with 

 more and others with fewer than the typical number of floral 

 whorls. The latter are always symmetrically arranged, the car- 

 pels always three or more and distinct, and the seeds contain 

 little or no endosperm. To this group belong the Frog-bits, 

 Vallisnerias, Water-Plantains and Triglochins. 



(B) The Glumiflorae are either destitute of a perianth, or 

 have a very rudimentary one, and not infrequently the stamens 

 and pistils are reduced in number ; the flowers are enclosed in 

 scaly or glumaceous bracts, and they are usually arranged in 

 spikes or panicles. To this group belong the Grasses and 

 Sedges. 



(C) The Spadicifiorae or Nudiflorae, as they are also 

 called, bear clusters of small, numerous, usually diclinous flowers, 

 having an inconspicuous perianth, or sometimes none at all. The 



