270 W. G. FARLOW. 



ance of the root, a bud appears on the base of the leaf- stalk, 

 looking towards the concavity, and from this grows the stem 

 (fig. 4, s). As a rule, the leaf is tolerably far advanced 

 in its development before the root appears, and the root in- 

 variably precedes the stem-bud. The terms forward and 

 backward with relation to the concavity of the prothallus are, 

 of course, inapplicable when the young plantlet is formed at 

 or near the end of a process of the character above described, 

 when the leaf and root shoot out ad libitum. In all cases a 

 vascular bundle traverses the leaf and root, and these 

 are in connection with the vascular bundle of the pro- 

 thallus. 



If now we compare PI. XI, fig. 10, Avith fig. 257, in Sachs's 

 * Lehrbuch der Botanik,' p. 346, which represents a longi- 

 tudinal section of a prothallus and a normally developed 

 embryo attached, we shall clearly see that the cases we have 

 been discussing diifer widely from the ordinary cases of 

 embryonal growth. Fig. 10 represents a longitudinal section 

 through the spot where a young plantlet, such as we have 

 described, shoots out from the prothallus {p,p), b represents 

 the leaf, r the root, and s the stem-bud, which was cut a little to 

 one side of the median line. First, at a glance, the figure in 

 Sachs's 'Lehrbuch' differs from fig. lOin thefact that the young 

 plant in the latter case is so intimately connected with the pro- 

 thallus that one cannot decide where the one begins and the 

 other ends; while, in the former, it is perfectly easy to trace the 

 outline of the young fern. Secondly, we have in the former a 

 structure known as the foot, f, by which the developing fern is 

 separated from the prothallus — a structure to which we find 

 no equivalent in fig. 10. Thirdly, the vascular bundle of the 

 plantlet is in direct connection witli vessels which lie wholly 

 in the prothallus. Fourthly, the order of evolution is different 

 in the two cases. In the one, the leaf arose first, as we saw, 

 and was tolerably well developed before a root and afterwards 

 a stem-bud made their appearance. In the other the root 

 anticipates by far both the leaf and stem-bud in its develop- 

 ment ; and, in fact, the root and stem are not produced from 

 the leaf-stalk, but (and this fact is not to be learned from 

 the figure, but from the accompanying description in Sachs) 

 by the subdivision of a single cell into four, one of which 

 forms the foot. 



So far as I know, a budding similar to that in the cases 

 described is only mentioned by Wigand,' Botanische Zeitung,' 

 Feb. 16, 1849, and by him in language which, it must be 

 confessed, is not a little obscure : — " Eine beachtenswerthe 

 Erscheinung begegnete mir bei einigen Exemplaren, namlich 



