212 



THIRD GROUP. VASCULAR CRYPTOGAMS. 



in Blechnum hastatum a lateral bud is formed beneath every leaf and becomes a 

 stolon 1 ); in Tree-ferns the terminal branching of the stem is reduced to a minimum, 

 either not occurring at all or only in abnormal cases. 



The formation of adventitious buds which do not originate in the terminal 

 branching of the stem is connected in the Ferns with the leaves, and in many cases, 

 in Ceratopteris, for instance, there is no terminal branching at all, and buds are formed 

 only on the leaves. These buds appear on the stalk or on the lamina of the leaf. 

 Such shoots in Pteris aquilina (Fig. 160 K) are on the back of the leaf-stalk and near 

 its base; in Aspidium Filix-mas (Fig. 158) they appear some way above the insertion 

 of the leaf, usually on one of the lateral edges of the leaf-stalk ; in both cases they are 

 formed according to Hofmeister on the young stalk before the development of the 

 lamina and before the differentiation of its tissue ; a single superficial cell of the stalk 

 is the mother-cell of the new shoot ; as the surrounding tissue grows up round it like 

 a wall, the bud may as in Pteris be sunk in a deep depression and there remain 

 dormant for some time ; in that case the leaf-stalk continues succulent and filled with 



FIG. 159. Aspltnium decussatum. Middle portion of 

 a leaf; the midrib st bears the leaflets /, at the base of which 

 the bud k has formed and has already put out a root. 



FIG. 160. Pteris aquilina. A the extremity of a stem st, the 

 apex of which is at ss ; near it at * a rudiment of a leaf, bs the 

 stalk of a leaf in its second year, at h its lamina concealed by hairs, 

 k a bud at the back of the leaf-stalk, -w roots. B young leaf in its 

 second year; bs its stalk, / its small lamina freed from hairs. 

 C longitudinal section of a similar leaf with the transverse section 

 of the stem st attached ; bs and / as in B. D the lamina of a leaf in 

 its second year seen from the front, i.e. on the upper side. ,E the 

 horizontal longitudinal section of a bifurcation of the stem; ss s's 

 the two apices, aa brown epidermal tissue, bb brown sclerenchyma, 

 g vascular bundles. A, B, C natural size, D magn. about 5 times. 



nutrient substances for some way above the bud long after the leaf has died away, 

 and in Aspidium Filix-mas strong stems with numerous leaves are not unfrequently 

 found connected at their lower end with a leaf- stalk from an older stem. In many 

 cases, as in Slruthiopteris germanica, these buds from the leaf-stalk develope into long 

 underground stolons furnished with scale-like leaves, which turn upwards in their 

 growth at their free extremity and unfold a circle of foliage-leaves above the ground ; 

 in Nephrolepis undulata they swell into a tuber at their extremity. Adventitious buds 

 are formed on the lamina of the leaf, especially in many of the Asplenieae 2 ; in 



1 Mettenius, Ueber Seitenknospen bei Farnen (Abh. d. Kon. Sachs. Ges. d. Wiss. 1860). 



2 On the formation of these buds see Heinricher in Sitz.-Ber. d. Akad. d. Wiss. in Wien, 1878. 



