Tissues in Certain Monocotyledons. 23 
He endeavoured to show that the so-called tracheides are 
no tracheides at all, but short vessels produced by the fusion 
of longitudinal series of cells. A certain amount of sliding- 
growth at the ends of the vessels was however recognized. 
The stages of cell-fusion were not only described, but figured, 
by Kny. One of us (D. H. Scott) made some observations, 
which appeared at the time to confirm Kny’s conclusions 1 , 
which were further accepted by Strasburger, in the second 
edition of his Botanisches Practicum 2 . Independent evidence 
for the origin of these elements by cell-fusion was next brought 
forward in a paper by Mdlle. Hedwig Loven 3 . This observer 
also claims to have followed the stages of cell-fusion. Stress 
is further laid on the number of cells found in the transverse 
section of the bundle while in the merismatic condition. 
The number was found to be higher than that required by 
Krabbe’s theory. Occasional, though very rare, traces of 
transverse walls in mature tracheides were also described. 
So far there appeared to be a balance of evidence in favour 
of the origin of these tracheae by cell-fusion. In 1889, how- 
ever, an elaborate paper appeared, by Roseler 4 , containing the 
most complete account of the subject hitherto published, and 
bringing forward weighty arguments in proof of the develop- 
ment of these elements by the growth in length of single cells. 
Roseler attacked the question from every side, but his most 
convincing evidence was obtained by means of maceration. 
In a species of Yucca which he investigated, the average 
length of the mature tracheide is 3 mm. ; and that of a cell 
of the secondary desmogen is o-i mm. Hence, on the average 
each desmogen-cell which becomes a tracheide must grow to 
thirty times its original length if no cell-fusion takes place. 
1 Annals of Botany, iv. p. 157, 1889. 
2 1. c. p. 125, 1887. 
3 Om Utvecklingen af de sekundare Karlknippena hos Dracaena och Yucca ; 
Bihang till Kongl. Svenska Vetenskaps-Akad. Handlingar, vol. xiii. 1887. For 
a translation of parts of the Swedish text we are indebted to the kindness of 
Mr. L. A. Boodle, F.L.S. 
4 P. Roseler, Das Dickenwachsthum u. die Entwicklungsgeschichte der 
secundaren Gefassbiindel bei den baumartigen Lilien ; Pringsheim’s Jahrbuch., 
Bd. XX, 1889, p. 292. 
