252 



like catkins, which are composed of a number of angular peltate scales, 

 spirally arranged round a central common stalk or axis, to which each 

 is attached by a short pedicel. Seated round the margin of each of 

 these scales, on its inner or under surface, are from four to eight ob- 

 long membranous cells or thecae, opening inwardly and longitudinally, 

 and discharging numerous somewhat globose sporules, to each of 

 which are attached, at one point, fom* spiral filaments ; the filaments 

 are dilated at the extremity, and they are generally more or less 

 studded with small granules. Hedwig and other observers hare 

 described these filaments as stamens, looking upon their dilated ex- 

 tremities as the anthers, and supposing the minute granules to be the 

 pollen. The filaments are at first wound spirally round the sporules, 

 but when discharged fi:om the theca suddenly unroll themselves, and 

 cause the sporules to leap about as if alive. The curious motions of 

 the sporules are owing to the structm'e of the filaments, which are 

 excellent hygrometers, being twisted like the awns of Avena fatua or 

 animated oat, and many other grasses, and are influenced in the same 

 way by the varying degrees of moisture in the atmosphere. 



Mr. Henderson's observations were made on Equisetum hyemale; 

 and he describes the changes which take place in the various parts of 

 the fiructification, from the first appearance of the catkin above the 

 terminal sheath of the stem up to the discharge of the mature sporule 

 from, the theca. 



" When tlie spike or fructification of Equisetum hyemale begins to swell beyond 

 the terminal sbeatb, the spores may be observed in a rudimentary state on carefully 

 dissecting the theca, the interior of which is at this time divided into cells of extreme 

 tenuity, in which the spores originate. These cells are filled with a viscid, greenish- 

 coloured fluid, which, when mixed with a small portion of water and highly magnified, 

 will be found to contain innumerable minute granules, possessing spontaneous motion, 

 and moving apparently on their axes with considerable rapidity : they are of various 

 sizes and of various shapes, the larger generally oblong, the lesser spherical : they are 

 all equally active, and being transparent, they communicate a whitish colour to the 

 water when viewed with the naked eye. * * It is extremely difficult at this 

 time to detach any of these cells entire, owing to the filmy condition of the walls and 

 the viscid nature of their contained fluid : a better opportunity is afibrded of viewing 

 their form and arrangement, by macerating the theca in dilute nitric acid, when they 

 appear somewhat shrunk and collapsed, and the minute granules are therefore easily 

 discernible in the cells and also in the spores : the whole mass is easily forced asunder 

 even to the theca, which separates into parts con-esponding with the sides of the outer 

 cells."— p. 568. 



The next stage in the progress of the sporules, namely, their tran- 

 sition from the granules with which the cells are at first filled, to the 



