84 EXTRACTS AND ABSTRACTS FROM FORFIGN JOURNALS. 



substance, are formed ; these latter cells represent the mother-cells in 

 which the pollen is generated. Besides these the antheroid mass has at 

 this time two descriptions of cells ; on one side the primordial colourless 

 cells; on the other, grey or yellow cells, generally provided with a nu- 

 cleus. The mother-cells soon become dark, as they fill with numerous 

 granules, in which one or two granular nuclei appear. These granules 

 coalesce in the centre of the cell, so that a transparent space is left 

 around them ; they then disappear, leaving the nuclei in the centre. 

 These nuclei are separated from each other at first by a fluid, which 

 afterwards becomes firm, forming distinct walls between them, during 

 this time also the walls of the mother- cells have been getting thicker ; 

 the nuclei continue to increase in size, become of a spherical form, and 

 are surrounded with a yellowish mamellated case ; as the walls of the 

 mother cells and the separating membranes disappear, they become free, 

 and produce perfect granules of pollen. No spiral cells or fibrous struc- 

 ture are developed in the endothecium. In the female flower, three 

 months after impregnation, the nucleus first appears as a very small 

 conical body, lying at the bottom of the ovarial cavity, accompanied by 

 one or two small club-shaped filaments, which are abortive nuclei. The 

 nucleus grows very rapidly, and has at its point a small spot indicating 

 the embryo, which is developed like the embryo of other dicotyledons, 

 there being, however, no quintine or embryo-sac. The only covering is 

 the remains of the nucleus or nuclear-sac, which increases in size, be- 

 comes firmer, and forms a green- coloured perisperm. 



Mohl on the Structure of the Stem of Isoetes lacustris. Whilst the 

 upper flattened leaf-covered surface of the spheroidal or bulb-like stem 

 presents nothing peculiar in appearance, the under one is seen to be 

 traversed by a furrow or slit, which extends to both sides, and as high 

 up as the insertion of the leaves ; so that the stem consists of two 

 spherical or bulb-like masses, connected by a commissure. The radicles 

 which are found in this furrow are not developed like those of other 

 abbreviated stems (bulbs, premorse roots, stems of other cryptogamia 

 and monocotyledons) in regular succession, so that the radicles seated 

 on the lowest portion are the oldest, but the new ones break through 

 the whole length of the furrow in its deepest part, they are therefore 

 placed in a semilunar manner, the points of the figure which they repre- 

 sent pointing to the insertion of the leaves. Probably every year the 

 stem loses an external coat, whilst a new layer is formed in the centre. 

 From the very minute woody system of the stem, a great quantity of 

 delicate unbranched and non-anastomosing vascular bundles are found 

 radiating. From the upper ones there proceeds an arched bundle, both 

 to the upper and under surface of each leaf ; from the lower there 

 passes a bundle to each radicular filament. The whole white mass of 

 the spherical stem consists of parenchymatous cells arranged in rows 

 parallel with the vascular bundles, filled with amylum, arid between 

 which run large intercellular passages. The external cells lie more 

 parallel with the surface of the sphere, contain very little, or even no 

 amylum, and form a peculiar, though not very distinctly defined layer, 



