172 HOPMEISTER, ON 



the principal branches, bring to mind most forcibly the 

 leaves of Trichocolea tomentella. The pro-embryo of Phas- 

 cum serratum is also remarkable, especially when it 

 originates from the loAver leaf-axils of developed plants. 

 It is a fact, noticed especially by Nageli, that the shoots of 

 the pro-embryo are often subterraneous for a considerable 

 distance 5 the transverse septa of such subterranean threads 

 of the pro-embryo are not perpendicular to their cylindrical 

 outer surface, but strongly inclined to it. The pro- 

 embryonal threads of Scliistostega osmundacea creep about 

 for a considerable distance in the damp sand upon which 

 this delicate moss is accustomed to vegetate. These sub- 

 terranean rows of cells have such a narrow cavity, and their 

 fluid contents are so transparent, and so deficient in 

 granular matter, that they may be mistaken for some of 

 the most delicate microscopical forms of moulds. When 

 the terminal cell of such a thread is exposed to daylight, it 

 immediately swells to a spherical form, and some beautiful 

 emerald green chlorophyll-bodies are formed in its fluid 

 contents. It would seem that a single chlorophyll-body is 

 first formed, which is then increased by self-division 

 (PL XVIII, fig. 16). The multiplication of the cells of the 

 subterranean green portion of the pro-embryo, takes place 

 by the continual division of its cells by means of transverse 

 septa. The process is somewhat peculiar. The new septum 

 does not pass through the mother-cell transversely, but the 

 division commences by the protrusion, from the apex, of a 

 small swelling which is at first hemispherical. The upper 

 part of this protuberance increases rapidly in circumference, 

 and becomes spherical ; the lower part, on the other hand, — 

 viz., the place of junction of the protuberance with the 

 mother-cell, — widens to a very small extent, or not at all. 

 Finally, when the size of the protuberance has nearly reached 

 that of the mother-cell, a transverse septum is produced at 

 the point of constriction, which cuts off the protuberance 

 from the mother-cell (PI. XVIII, fig. 16). Some time 

 before the appearance of this septum, the first chlorophyll- 

 vesicles are perceived within the protuberance. Usually 

 only one such vesicle is at first visible, and the first symp- 



* ' Zeitschrift fur Wiss. Bot.,' Hft. 2, s. 172. 



