Tissues in Certain Monocotyledons . 31 
fewer stages of development were met with in each series. 
But so many young tracheides were observed at various 
stages of elongation, and always with a single nucleus, 
that there could be no doubt of their development by 
growth alone. 
The results obtained from sections were confirmed by the 
method of maceration. The ordinary Schulze’s mixture 
(nitric acid and potassium chlorate) was used. Thick tan- 
gential sections through the zone of secondary growth were 
treated with the reagent, and it was then found possible, in 
many cases, to isolate the elements of the developing bundle. 
In Fig. 2 a young tracheide of Yucca sp. is shown, which 
had only reached about a quarter of its mature length (7 25 
mm.). The single large nucleus is conspicuous. Some 
desmogen-cells of the same strand are shown for comparison. 
Fig. 3 represents a young macerated tracheide of Dracaena 
fragrans. Here the average length of the mature tracheide 
is 3*15 mm. ; that of the young element shown is *95 mm. It 
is obviously uninucleate. Here again desmogen-cells are 
shown for comparison. These results require no long de- 
scription, as they simply repeat those obtained by Roseler. 
Krabbe, Kny, Mdlle Loven, and Roseler, all lay great 
stress on the results obtained by counting the elements of the 
bundle, as seen in transverse section, at various stages. If 
the tracheides were formed entirely by cell-fusion it is obvious 
that the number of elements in the transverse section of the 
desmogen-strand, after the completion of its divisions, would 
be the same as in the mature bundle. If however the 
tracheides arise by elongation of single cells, the desmogen- 
strand must contain less than half as many elements as the 
mature bundle, in transverse section. Thus in our species of 
Yucca the average number of elements seen in mature bundles 
is sixty-six (neglecting the sheath). Of these, thirty- six are 
tracheides. The strand of desmogen when its divisions are 
completed must therefore show an average number of sixty-six 
elements on Kny’s view. As, however, on the opposite sup- 
position, only one cell at each level grows out to form a 
