Notes. 
487 
case in one of the Roscoea seedlings examined. It is, therefore, evident that the 
presence of centripetal wood in one vascular strand of the cotyledons of Brachychilum , 
Roscoea, and A Ipinia , is due to the fusing of two small cortical bundles after they have 
become closely associated with the main strand, but before they are wholly merged 
in it. 
It must be added that there is a tendency for large single tracheides to occasionally 
make their appearance on the side of the protoxylem remote from the metaxylem 
throughout the whole course of both bundles, but this is to be observed in the cotyle¬ 
dons of many monocotyledonous families. In Anemarrhena isolated tracheides occur 
scattered between the two bundles, and in Erythronium grandiflorum , where there are 
several laterals, their appearance usually precedes the fusion of two of these ; in Iris 
the single strand of fused bundles ends in a brush of these spirally thickened 
elements, while in Maianthemum a group of three tracheides was observed in the 
ground tissue quite apart from any vascular bundle. 
In an organ whose most important function is the rapid passage of food 
substances to the growing plant, the occurrence of such elements is likely to'be 
an adaptive feature rather than a primitive one, and their frequent but by no means 
constant association with the bundles in a centripetal position does not necessarily 
indicate their vestigial nature. 
Summary. The well-marked mesarch structure of one of the cotyledonary 
strands in the lower part of the sucking cotyledon of certain Scitamineae is evidently 
due to the relative movements of the constituent bundles after they have become 
associated together in a single strand, and is therefore of no phylogenetic im¬ 
portance. 
E. M. BERRIDGE. 
PRELIMINARY NOTE ON APOGAMY IN PTERIS DROOGMANTIANA. 
—A cytological investigation of the prothallus of this Fern has revealed features of 
much interest. In the young prothallus, cells each containing two nuclei are common : 
it appears certain that in this form neither of the paired nuclei has migrated from an 
adjacent cell, as in every case a nucleus is present in each of the surrounding cells. 
Our available evidence indicates that the pair of nuclei are formed by the division of 
the nucleus of an ordinary cell, no cell-wall being laid down between the daughter- 
nuclei. After division has taken place the two daughter-nuclei remain for some time 
unfused, but, in most if not all cases, fusion eventually takes place. Stages in the fusion 
have been observed, and the resultant nuclei are very large and at first often lobed. 
We are indebted to Mr. Boodle for kindly supplying us with material for 
examination. 
E. L. STEPHENS. 
M. G. SYKES. 
