34 Scott and Brehner .—On the Secondary 
the strand often gives it just the same shape as if it had 
arisen by cell-fusion. When it bends aside to pass from one 
tier of cells to the next it is often constricted, and an oblique 
wall lying over it at such a point may easily simulate a 
perforated septum. Confusion of the very young sieve-tubes 
with developing tracheides is also possible, and would of 
course suggest cell-fusion. Accidental tearing of the delicate 
end-walls of the desmogen-cells may also give rise to decep- 
tive appearances. The idea that the tracheides are multi- 
nucleate may have arisen partly from the confusion of 
coincident elements in different planes, partly from the 
presence in the tracheides of coagulated masses of protoplasm, 
which might be easily mistaken for nuclei. We know from 
our own experience that all these cases are possible sources 
of error ; but we cannot undertake to explain how other 
observers may have been misled. In Kny’s Fig. 2, PL XIV, 1 
the long element to the right may probably be a developing 
tracheide, though not recognised as such by the author. 
Appearances suggestive of cell-fusion are rare, and are 
most frequent in the least satisfactory preparations. We are 
convinced that such appearances are in all cases illusory. 
We hope that the question may now be regarded as 
definitely settled, and that one of the most striking cases of 
sliding-growth in the development of vegetable tissues has 
thus been firmly established. 
II. Secondary Growth in thickness of the Roots 
of Dracaena. 
Until the year 1884 our knowledge of the development of 
secondary tissues in the roots of Monocotyledons was very 
meagre. The earliest account known to us is that given by 
Caspary in 1858 2 . He examined several species of Dracaena , 
and states that the cambial layer of the root lies between the 
c Schutzscheide 5 (endodermis) and the central mass of vascular 
bundles ; in modern terminology the cambium observed by 
1 1. c., Berichte d. deutsch. bot. Gesellsch. IV. 
2 Die Hydrilleen ; Pringsheim’s Jahrbiich., Bd. I. p. 446. 
