396 HOFMEISTER, ON 



commencement of the formation of the first axis — which 

 takes place by division of the terminal cell of the short pro- 

 embryo by alternately inclined septa — is usually preceded 

 by the division (from once to three times) of the terminal 

 cell of the bicellular pro-embryo (embryo-bearer) by trans- 

 verse septa. During this process a very considerable 

 longitudinal expansion of the upper cells of the pro-embryo 

 takes place, in consequence of which its lower end is pushed 

 deep down into the tissue of wider cells, which tissue in 

 S. hortensis now fills about a third part (PL LVIII, fig. 4), 

 and in 8. Martensi the whole of the cavity of the spore. 



By the multiplication in manner above mentioned of the 

 terminal cell of the pro-embryo, the first axis of the embryo 

 is formed. In 8. hortensis, after a very short longitudinal 

 development, the number of the cells of this axis increases 

 no further ; on the other hand an adventitious axis shoots 

 out from one of its sides destined to break forth from the 

 prothallium and to produce the first pair of leaves of the 

 embryo (PL LVIII, figs. 7 — 10). The form of the growing 

 end of this shoot, as well as the mode of its cell-multiplica- 

 tion, is exactly that of the subsequent vegetative axes above 

 described. Its growth is directed obliquely upwards. 

 During its longitudinal development, the end of the primary 

 axis of the young plant, which in 8. hortensis is hitherto 

 hardly perceptible, increases somewhat in size, more by the 

 expansion of its cells than by their multiplication (PL LVIII, 

 figs. 7, 10). 



Before the shoot of the second order has pierced through 

 the lower, wide-celled layer of the prothallium, it produces 

 two opposite leaves, by the contemporaneous division of 

 horizontal rows of cells of its wide lateral surfaces. After 

 the shoot has emerged to the light these leaves are developed 

 and produce chlorophyll in their cells. The arrangement 

 of their cells exactly corresponds in all stages of develop- 

 ment with that of the primary leaves of vegetative shoots. 

 In the germ-plants of all the species which I have seen, 

 these leaves bear appendages on both sides of their base. 

 In their axils adventitious leaves are formed, precisely 

 similar to those produced at a later period (PL LVII, 

 fig. 22). Not long after the appearance of the first pair of 



