Doyle — Some Researches in Experimental Morphology. 425 



ia the cells of the medulla, although the cambium cells also become active, 

 and give rise to much parenchyma. Needless to say, the whole tissue is 

 packed with storage material. 3. The formation of tubers in Oxalis crassi- 

 caulis is brought about by the development of stolons, which run out, the 

 apices forming tubers. These stolons carry very small buds and leaves, so 

 small, indeed, that only with a good lens can the petiole and lamina be dis- 

 tinguished. If the apex is removed, and also the buds, the cut end of the 

 stolon swells ; but likewise all that part of the small leaves which corresponds 

 to a petiole develops into a tuber. 4. A leaf of Raphanus satmis v. radicula 

 when rooted developed no buds, and but few roots. The base, however, 

 swelled to a tuberous formation, mainly derived from the old cambium. Here 

 we see tubers functioning as stems and contra tubers, resulting from the active 

 division of the parenchymatous cells of old stems and leaves. 



For such apparently stable organs as leaves, there are a large number of 

 instances of abnormal tissue development in them. Thus Mer (19) mentions 

 an ivy leaf which he rooted, and kept growing for seven years. The petiole 

 bundles enlarged radically to three or four times their original size, due to 

 the activity of the old cambium. We may also mention that he observed an 

 increase in the palisade tissue. 



Recently Mathuse (20) describes a large number of very similar results 

 with rooted leaves, usingabout twenty from fifteen different orders. His results 

 varied, but in most cases he got increased secondary thickening in the petiole, 

 and very frequently increased palisade tissue. As far as can be deduced from 

 his sketches, his secondary development never exceeded our Sol. Richardi 

 leaf grafted on Lycopersicum (Plate XXXIII, fig. 4). In one case, how- 

 ever — Achryanthes Verschaffelti — he describes how the base of the petiole 

 hypertrophied, due to active divisions of the parenchyma, giving a mass of 

 small cells starch-packed, just like the leaves of Pelargonium zonule, or those 

 of Raphanus, mentioned by Vochting. 



Interesting is the work of Freundlich (21), who cut the main nerves of 

 the cotyledons and foliage leaves of various Dicotyledons. Not every plant 

 was suitable, but in several cases — most neatly in Fittonia argyroneura hort. — 

 leaving the cut end nearer the apex, bridges of tracheides grew out, being 

 formed in the parenchymatous tissue round the end of the bundle. These 

 actually grew out round the cut, and formed anastomosis with the bundle end 

 below the cut, or with neighbouring large branches. Simon (22) has given us 

 a most interesting paper on similar connexions formed in stems and roots in the 

 medullary tissue. In one of his most interesting experiments he cut across a 

 plant again, placed the parts in apposition, with a sheet of mica perforated in 

 the centre between them. In this way only at the medulla were the two 



