478 



LECTURE XXVII T. 



the normal maintenance of the plant : this is the case, for example, with many Ferns, 

 and with the runners and rhizomes of numerous other plants. 



The occurrence of adventitious shoot-buds is much rarer. It takes place chiefly 

 on fully developed or on young leaves. As particularly well-known examples may 

 be mentioned those in the indentation of the margin of the leaf of Bryophylhmi 

 calycinum, and the bulbils regularly formed in the angles on the ramifications of the 

 veins of the leaves of Cardamine pratejisis and Nasturtium officinale. Very striking 

 examples of such buds are found moreover in Ny??iphcca viicrantha at the centre of 

 the peltate leaf, and in various Aroideae — e.g. Atherurus ternatiis, where the 

 adventitious buds have the form of tubers or bulbs, which subsequently become 

 free and form new plants. In a considerable number of other Monocotyledons 

 and Dicotyledons also adventitious buds appear on the foliage leaves in the ordinary 



course of vegetation: these, however, so 

 long as the mother-leaf is actively vegetat- 

 ing, continue in the bud-state, as in the 

 cases mentioned previously. 



Adventitious shoots are particularly com- 

 mon on the large foliage leaves of the 

 Ferns, and they appear regularly in the 

 angles of the pinnatifid laminae of Ce7-a- 

 topteris thalictroides, and on the rachis 

 oi Aspleniiim caudatum, A. deciissatum, and 

 other species of this genus : they occur 

 also on the under side of the mid- rib of 

 Woodwardia radicans and others. In these 

 cases, as in Cardamine, they grow while 

 still connected with the mother-leaf into 

 vigorous copiously branched plants, which 

 sooner or later become free from the 

 mother-leaf and can at once proceed to 

 active vegetation. Among the most in- 

 teresting examples of this kind we have 

 moreover the formation of adventitious buds on the back of the living basal portions 

 of the older foliage leaves oi Aspidium ßlix-7nas {i\iQ common Male-Fern), for this 

 plant developes no lateral buds whatever except these adventitious shoots (which are 

 moreover very isolated) and possesses no normal branching. It has already been 

 stated in the introductory lectures on Organography that adventitious shoots are also 

 developed not rarely from the roots of vascular plants, and new independent plants 

 then proceed from these : this is the case, for example, in Robinia, Ailatithus, and also 

 in the Fern Ophioglossimi. To these cases also we may in a certain sense refer the 

 production of shoot-buds from the growing-points of roots, as mentioned on p. 22. 



In opposition to the view formerly held by Hofmeister, that all adventitious 

 growing-points arise in the interior of the tissue, and that all so arising are to be 

 designated adventitious, it is to be noticed that in that case almost all roots would 

 have to be regarded as adventitious. With respect to adventitious shoots it is demon- 

 strated by recent investigations, and especially those of Hansen on Carda?nine, 



Fig. -i^b.—Asplenium dectissatum. Middle portion of a 

 fully developed leaf the rachis st of which supports the pinnules 

 // ; at the base of one of these has arisen the bud k which has 

 already put forth a root (nat. size). 



