334 HOFMEISTEB, ON 



place suddenly and at right angles * to the surface of the 

 first leaf the first leaf arid the principal bud are carried 

 upwards out of the fissure (PL XLV, fig. 27). The stalk- 

 like organ which hears the first scutiform leaf is therefore 

 not formed exclusively, or even mainly, by the longitudinal 

 extension of either the lower end of the embryo which lies 

 opposite to the entrance to the archegonium, or of the 

 primary axis, which in Salvinia is only very slightly deve- 

 loped. The hinder end of the embryo plays the principal 

 part in the formation of the above-mentioned stalk. 



The vascular bundles originate from the stalk. Never- 

 theless, the interior of the latter does not produce any 

 spiral vessels which pass immediately into the first leaf and 

 the stem above it (PI. XL\ r , fig. 28) ; here all the cells of 

 the bundle remain thin-walled. The second and the third 

 leaf are formed behind the ramifications of the principal 

 bud, without the occurrence of any new ramifications 

 (PL XLV, fig. 28, 29). Then, however, the less vigorous 

 branches become elongated (usually ramifying again at the 

 same time), and form the leafless branches, of limited 

 growth, which hang down into the water, and which have 

 been generally considered by the earlier writers as adven- 

 titious roots, f These brandies grow by the repeated divi- 

 sion of an apical cell by means of septa, inclined alter- 

 nately in two directions, and by the division of the cells of 

 the second degree by a radial longitudinal septum, and 

 then by a transverse septum perpendicular to the axis. 

 Afterwards the cells divide, by septa parallel to the axis, 

 into inner and outer cells, and this latter division is several 

 times repeated in the cells of the circumference. 



I observed myself what Savi had previously noticed 

 that microspores which had been carefully kept apart from 

 microsporangia developed a prothallium, but no embryos. 

 It is but rarely that two embryos are produced in the same 

 prothallium. I have only observed the occurrence twice. 



The Rhizocarpeee have always attracted a considerable 



* This direction forms an angle of about 30 with the longitudinal axis of 

 the embryo. 



f Mettenius has correctly described them, 'Beitr. zur Botanik.,' Heft i, 

 (Heidelberg, 1850) p, 15. 



