422 Scientific Proceedings, Royal Dublin Society. 



in its horizontal diameter 3'1 by -VO mms. in its vertical. The corresponding 

 measurement of the petiole after grafting was 6-4 x 7-7 mms. 



Plate XXXITI, fig. 1, is a photograph of the secondary development in 

 the bow-shaped bundle of Plate XXXII, fig. 4. It is taken at the very same 

 magnification. The primary wood of fig. 3 is seen here at [a). The presence 

 of well-developed thin medullary rays consisting of one or two layers of cells 

 can be seen. It gives us a good idea of the mass of wood developed in these 

 petioles. 



Similar results were recorded for Sol. RiehanU, but in both species one out 

 of tlie three or four grown to maturity had no development of wood from 

 the abnormal cambium. 



The changes in the other two leaves must next come under consideration. 

 In those plants B where a leaf was grafted on the main stem there always 

 appeared a re-awakening of the fascicular cambium. Thus, Plate XXXII, 

 fig. 1, shows us sucli in Pelargonium. But tliis development never 

 approached even remotely that of the petiole-made function as a stem. 

 Thus the greatest increase in any such was seen in a leaf of Solanum 

 Richardi' which was grafted on the stem of Solanum Lycopersicmn, Gloire de 

 Charjpenne. 



The normal petiole of S. Richardi is shown in Plate XXXIII, fig. 2. 



Plate XXXIII, fig. 3, shows the leaf after growing for three months 

 on the Tomato stem. It was only removed when it began to die. This 

 is at the same magnification as Plate XXXIII, fig. 2. 



Comparing Plate XXXII, fig. 4, and Plate XXXIII, fig. 2, at the same 

 magnification, we see that S. Richardi and S. Balhesii are very similar. 

 Looking now at Plate XXXIII, figs. 1, 2, and 3, all at the same magnification, 

 we can see how the maximum secondary wood development observed in these 

 B plants, compares with the normal primary wood and with the wood in the 

 petiole-made function as a stem, llemember, too, that Plate XXXIII, fig. 1, 

 is only part of one of the wood masses in the petiole. Interfascicular 

 cambium never appeared in this group. The petioles were always packed 

 with starch. 



In the D groups, i.e., leaves left on the stem whence the other leaves 

 and all the other buds had been removed, very little change was observed, 

 although tlic leaves grew for months before they died. In one ease out of 

 at least a dozen Pelargoniums a development up to about the same extent as 

 in the B group took place, but in only one. In the others never more than a 

 few tracheides were secondarily developed. In a few cases, however, active 

 divisions took place in isolated places in the cortex similar to those to be 



