a 
The Occurrence of Tracheides in the Nucellus 
of Steriphoma cleomoides, Spreng. 
BY 
MATTHEW YOUNG ORR, 
Assistant in Laboratory, Royal Botanic Garden, Edinburgh. 
With Plate CLXVI. 
THE occurrence of tracheidal elements in the sporogenous tissue 
of ovules has been recorded, up to the present time, in only three 
genera, belonging to families possessing no close phylogenetic 
relationship. 
They were first described by Treub* as occurring in the 
nucellus of Casuarina glauca, Sieb., and Casuarina Rumphana, 
Miq. As figured in his paper, they are elongated, narrow, 
pointed cells, and their production in the sporogenous tissue 
suggested to him an analogy with the formation of elaters 
in the Hepaticae. Their function he regarded as a matter 
for speculation. 
Miss Benson,7 in her investigations on the embryology of the 
Amentiferae, recorded the occurrence of small tracheides around 
the antipodal end of the embryo sac of Castanea vulgaris, Lam. 
She suggested that these elements were vestigial in character and 
that they represented some former organ—“‘ possibly a vascular 
strand connecting the chalaza with the sporogenous tissue.” 
The third instance is recorded by Frye f{ in his work on the 
Asclepiadaceae. In his examination of the ovule of Asclepias 
cornuta, Dec., he noted the presence of a tracheid near the base 
of the embryo sac, and slightly projecting into it. This author 
favours Miss Benson’s suggestion as to the origin of these 
tracheides, but is unable to reconcile their occurrence in a 
specialised family like the Asclepiadaceae with their supposed 
primitive character. 
While examining sections of the ovaries of certain Cappari- 
daceae, the author of this note observed the occurrence of 
elongated elements, with well-defined annular thickening on 
* M. Treub in Ann. du Jard. Bot. de Buitenzorg, x (1891), p. 170. 
+ M. Benson in Trans. Linn. Soc., iii (1894), pp. 412, 421. 
" - ms Frye in Botanical Gazette, xxxiv (1902), p. 402. 
(Motes, R.B.G., Edin., No. LX, January 1927-] | A 
Wt. By oon cares —N. & CO., ie 
