744 REPOKT— 1892. 



nuclear ' augmentation ' is as inexplicable on Rabl's doctrine as the ' reduction ' 

 described in (6). 



The author concludes that Eabl's doctrine of the personality of the nuclear 

 segments is not itself firmly enough established to serve as the foundation of any 

 wide-reaching theory. 



FRIDAY, AUGUST 5. 



The following Papers were read : — 



Defartment of Botany. 



1. A Proposed World's Congress of Botanists at Chicago in 1593. 

 By Dr. J. C. Aethub. 



2. Ohservations on Secondary Tissues in Monocotyledons. 

 By D. H. Scott, M.A., Ph.D., F.L.8., and George Brebner. 



1. Origin of secondary tracheides in Draccena and Yucca. 



Two contradictory views have been held on this question. On the one hand 

 Krabbe, Roseler, and Strasburger maiutain that these elements are true tracheides, 

 each arising from the elongation of a single cambial cell. On the other hand Kny, 

 Mdlle. Loven, and Wieler regard them as short vessels arising by the fusion of a 

 series of cambial cells. To this view one of tlie authors of the paper (Dr. Scott) 

 formerly inclined. 



A more complete investigation has, however, shown that the appearances 

 of cell-fusion are illusory, and that each tracheide develops simply by the enor- 

 mous growth in length of one cell. The nucleus usually remains undivided. The 

 tracheides have been observed, both in sections and in macerated preparations, at 

 all stages of their growth. The definite decision of this point is of interest, as 

 establishing some of the most striking instances of ' sliding growth.' These 

 tracheides often grow to forty times their original length, and that in a region 

 which, as a whole, undergoes no elongation. Thus the whole room required for 

 the growth of these elements has to be provided by mutual displacement of cells. 



2. Growth in thickness of the roots of Drnccena. 



When a cambium arises outside the vascular bundles it is usually formed in the 

 pericycle. In these roots we have a conspicuous exception to the rule, for here it 

 is quite common for the cambium to appear in the cortex, outside the endodermis. 

 In Dracana Draco, D./ragrans, and Z>. ensifolia the authors found that the cam- 

 bium is often formed in the cortex at once, without any previous pericyclic develop- 

 ment. The two modes of growth, however, often occur side by side, or combined 

 in the most irregular manner. Connecting vascular bundles, passing through the 

 endodermis, were often observed. 



A new point of importance is that in most cases observed, the secondary growth 

 starts from the insertion of a rootlet, advancing upwards and downwards, as well 

 as peripherally, from this place. At and near the insertion of the rootlet the cam- 

 bium is always pericyclic; at a distance from it cortical cambium begins to appear, 

 while at a still greater distance the pericyclic cambium disappears, and the forma- 

 tion of secondary tissues is limited to the cortex. 



3. Secondary thickening in Iridacece. 



The authors are not aware that any example of this has been described before. 

 Their attention was called by Professor Bower to the occurrence of secondary 

 thickening in Aristea corymbosa, Ait., an iridaceous shrub. The process has now 

 been fully investigated, and agrees generally with the Ih-acana type. The young 

 stem of Aristea is flattened in the plane of the distichous and equitant leaves. 

 The primary vascular cylinder is thus narrowly elliptical in transverse section. 



