Notes . 
355 
vascular bundles are larger than in the normal specimen, whilst the isolated phloem 
strands are replaced by small, complete vascular bundles. A final point of difference 
consists in the more complete development of the sclerenchyma zone in the 
abnormal specimen. It was better differentiated (more highly sclerized), and also 
consisted of more numerous cell-layers. The relative increase of this ‘ mechanical ’ 
tissue was greater than that of the ‘ vascular ’ elements. 
These modifications the writer attributes to the joint requirements of a flower 
scape which has to sustain and carry water to an extensive vegetative develop- 
ment, such as that represented in Fig. i- requirements which are both transpira- 
tory and mechanical. 
Some time ago, as a consequence of grafting buds on petioles of Pelargo- 
nium zonale , the writer found that when the buds grew into large plants the petioles 
developed secondary thickening, interfascicular cambium, periderm, and an indefinite 
extension of life (Proc. Roy. Dubl. Soc., vol. xiv, no. 33, 1915). In the paper cited 
he gave reasons for the contention that the secondary thickening in the grafted 
petioles was not entirely due to the stimulus of increased transpiration require- 
ment (as claimed for similar phenomena by Winkler in Jahrb. f. wiss. Bot., 
Bd. xlv, 1907), but also largely as a response to some mechanical stimulus from 
the obviously increased stresses to which the petiole was subjected. This con- 
tention seems to be borne out by the circumstances described for the case of 
Plant ago lanceolaia. 
JOSEPH DOYLE, M.Sc. 
Biological Laboratory, 
University College, Dublin. 
