MARSILEACEyE. 



I. P1LULARIA. 



The stem of Pilularia is creeping : it consists as it were of 

 two cylinders, at least when mature : The outer system is 

 chiefly cellular, the cells towards the circumference being di- 

 vided into air cells, which are disposed in a radiating manner : 

 the septa are composed of a single scries of cells : next to 

 these occurs a thin layer of fine fibrous tissue. 



The inner system is easily separable, it consists externally 

 of tubes of some diameter arranged in perhaps two series, the 

 central part, consists of ducts (not many) and fine fibres, the 

 central portion becomes subsequently discoloured, no spiral 

 vessels occur ; but the young parts should be carefully exa- 

 mined, as unrollable ducts occur in the petioles. 



The petioles have the same external cellular tissue with 

 similar air cells, the central part consists of tubes, and unroll- 

 able ducts, but these are few in number. 



Granules are abundant, especially about the tubular tissue 

 of the pedicells. 



Small stomata occur on both sides of the leaves, on the 

 petioles ?, and stem ?, venation dichotomous, the venules ir- 

 regularly connected : terminations simple. 



Hairs articulate. 



The cells of the cutis, especially those of the under surface 

 sinuose, the petioles are of a callous nature ! protected by 

 strong haris, buds subterminal, or obliquely situated with re- 

 gard to the axil of each frond, the fructification which is ge- 

 nerally fasciculate intervening. 



The radicles, pierce through the outer cellular portion, but 

 are not calyptrate, the branches communicate directly with 

 the centres ; not as in Azolla where they are formed by an 

 elongation of the cells of the circumference, young roots co- 

 vered near the base by a vaginiform sheath. 



