370 HOFME1STEE, ON 



features, the mode of growth of the terminal bud of the 

 three-furrowed species of Isoetes agrees with that of 

 Isoetes lacustris : the septa which appear in the apical cell 

 are turned towards the furrows of the stem. 



Isoetes lacustris as is well known*" exhibits occa- 

 sionally, but rarely, a three-furrowed stem. Transverse sec- 

 tions of the stems of plants of this kindf exactly resemble 

 those of Isoetes setacea. The lower part of the woody mass 

 has three short arms (PL XLVIII, figs. 6, 7). The mode of 

 multiplication of the apical cell of the terminal bud is ex- 

 actly the same (PI. XLVIII, fig. 8). 



Like the Selaginelke amongst the Lycopocls, Isoetes, in its 

 mode of reproduction, resembles more indeed than any 

 other cryptogam that group of phsenogams which comes 

 nearest to the cryptogams, viz., the Coniferae. The pro- 

 thallium, which consists of cells devoid of chlorophyll, 

 occupies a space not much greater than the macrospore 

 itself. It originates by free cell-formation in the interior 

 of the spore-cell. In both respects it comports itself in a 

 manner precisely similar to that of the albuminous body of 

 the Coniferae. The archeo'onia of Isoetes in the most 

 essential features of their development and structure ex- 

 actly resemble the corpuscula of the Coniferse. 



Amongst the dioecious cryptogams the cryptogams 

 with spores of two different sizes, of which the larger pro- 

 duce the germs of the second, spore-bearing generation, 

 and the smaller produce the spermatozoa by which the 

 germs are impregnated Isoetes exhibits more clearly than 

 any other the necessity for the operation of both kinds 

 of spores in the process of reproduction. In Pilularia and 

 Marsilea the reproductive cells are surrounded by an 

 abundance of mucilage, which hinders the examination of 

 the spermatozoa, a state of things which occurs in many 

 of the lower plants and animals of the most different kinds. 

 In Salvinia observation is impeded by the firm adhesion 

 of the small spores, and by the difference in the time of 

 development of the microspores and macrospores when sown 

 contemporaneously. In Isoetes, on the other hand, the 



* A. Braim, ' Flora,' 1847, p. 34. 



f Amongst more than 100 specimens I found only one of this kind. 



