132 



PRINCIPLES OF PLANT-TERATOLOGY. 



as the plum and elm, a normal, constant feature of the 

 plant, in the same way in certain plants adventitious 

 shoots on leaves have become a fixed and normal 

 characteristic, as in Bryopkylhim calycinum and the 

 orchid MaJaxis paludosa, where they occur all round 

 the margin of the foliage-leaves ; in other species of 

 the first-named genus they do not occur ; in one 

 species a shoot was observed seated in the notch at 

 the tip of one of the cotyledons ; another occurred on 

 the top of the petiole ; on neither of the two young 

 foliage-leaves already formed were any buds present. 



The ladies' smock {Garcia mine ijratensis) is well 

 known to form great numbers of adventitious shoots 

 on its foliage-leaves at the base of the leaflets ; several 

 other species of the genus do the same. They are also 

 well known to occur in other members of the section 

 Arabidese, e.g. in the water-cress (Nasturtium officinale), 

 and in a species of rock-cress (Arabis piimila). With 

 the exception of the last-named, all these plants grow 

 in moist habitats, and the environment has probably 

 something to do with the anomaly. 



In Tolmidea Menziesii adventitious shoots are often, 

 and apparently as a normal feature, formed in the 

 sinus at the base of the leaf-blade, a character which 

 appears to become accentuated under cultivation. In 

 all three of the British species of sundew (Drosera) 

 such shoots are frequently developed on the upper 

 surface of the blade (PI. IX, fig. 3). But by far the 

 most remarkable case of this sort is afforded by Begonia 

 pliyllomaniaca (probably a cross between B. manicata 

 and B. incarnata) in which the surface of the blade and 

 petiole is thickly sprinkled with buds in all stages of 

 development. In one of the parents, B. manicata, as 

 also in some other species, the surface of the blade and 

 petiole along the veins is clothed with brown scale- 

 leaves; the formation of such a scale-leaf may perhaps 

 be regarded as the first arrested stage in the develop- 

 ment of an adventitious shoot, which has become a fixed 

 character of the species. It is a similar phenomenon 



