* THE STEM Oil SHOOT. 



137 



replacing the whole of the upper part of the leaf, viz., 

 the higher part of the petiole and the leaf-blade, may 

 in some sort be compared with the terminal position 

 of the adventitious shoot on the roots of Neottia and 

 certain ferns. In the case of the Pelargonium the 

 petiole, in spite of the remarkable internal changes 

 which it undergoes, still remains a petiole, and can 

 only be regarded as changing into a stem from the 

 purely physiological and functional point of view. 

 In the same way as the adventitious occurrence of 

 tracheicles, sporangia, or a sporophytic shoot on the 

 prothallus of a fern cannot surely be held to prove an 

 homologous relationship between the prothallus and 

 sporophyte. 



Bulb-growers often propagate bulbs, e. g. those of 

 the hyacinth, by deeply scooping out the base of the 

 bulb so that the fleshy scale-leaves are cut through, 

 when, at the margins of the cut surfaces abundant 

 young bnlbs are formed. Some bulbous plants, e.g. 

 J j ilium sp., are propagated from single bulb-scales ; 

 in the same sort of way as the fleshy leaves of some 

 species of Sedrim ; and, doubtless, other Crassulaceas 

 will also produce young plants when isolated and 

 placed in sand. 



A bul-b of hyacinth affected with the crown-gall 

 disease (caused by Bacterium tiimefacievs) was greatly 

 hypertrophied, due to the abundant formation in all 

 parts of the bulb-scales of small bulbils, more or less 

 irregularly and imperfectly formed. Just the same 

 kind of structure has occurred in a bnlb of Scilla 

 sp., but in this case the hypertrophy may be attributed 

 to a mite which was found in plenty on the affected 

 part. 



A bulb of the wild hyacinth (Scilla festaUs) was 

 also seen to have proliferated to form a second bulb 

 at a considerably higher level. As this second bulb 

 consisted entirely of thickened scale-leaves and was 

 devoid of a central axis, the lateral bulblets formed by 

 it, instead of arising, as in the lower bulb, in the usual 



