363 
Ke?idrickia Walkeri, Hook. f. 
characteristic of other Melastomaceae, 1 is a most striking feature, both 
in the parenchyma and in the thick-walled xylem, of the secondary 
thickening in Kendrickia. 
In stems of about this same age the formation of tylosis is of exceed- 
ingly common occurrence. It takes place not into old or damaged xylem- 
elements, but through the pit-membranes of normal, often newly formed 
tracheids and vessels (Fig. 6). Occasionally in stems of this age the 
tylosed cells may develop into sclerotic cells. Although thickening of the 
cell-wall, with pit-formation, is of fairly common occurrence in tylosed 
cells, yet actual development into sclerotic cells is somewhat rare. Haber- 
landt 2 cites a few cases in which such a development occurs. 
The fact that tyloses are thus prominent features in the still com- 
paratively young stem is of considerable interest, when viewed in the light 
of the changes which take place in the older stems to be described later. 
In most instances this wedge-formation goes on coincidently with the 
rest of the secondary thickening, and no further changes are observable 
until the stem has gained considerably in thickness. The size of the 
stem, however, is not always an indication of the extent of the internal 
changes. Occasionally a stem of small diameter may have a much more 
complicated internal structure than one of much greater diameter. 
It is after the stem has acquired the structure above described that the 
apparently mature cells of the secondary zone of thickening begin to show 
a rather abnormal development, which takes origin in one or several cells, 
at the central margin of the parenchymatous wedges. These cells take 
upon themselves new growth, and enlarge or dilate laterally and in 
a central direction. This enlargement is accompanied by cell-division, 
and the resulting cells then proceed to encroach upon the hard xylem 
area,, and, as is evident from the figures, this may take place in either 
of two ways. In Fig. 7 the process has been one of penetration of paren- 
chymatous projections, between the contiguous walls of xylem-elements, 
by means of which adjoining rows of tracheids have been split apart. 
In this figure it is found by counting from left to right that there are 
ten rows of parenchymatous cells and ten rows of tracheids. The new 
growth from the cells of the third row of the wedge, which is shaded in the 
figure, has penetrated between the third and fourth rows of tracheids, 
in the first instance to the extent of three cells deep, then, having separated 
the second and third tracheids of this fourth row, has proceeded to inter- 
polate the product of its division, between the fourth and fifth rows, until 
there is a direct parenchymatous connexion between the wedge (a) and the 
patch ( h ). In this case tylosis has played no part whatever, and, as is 
evident from the figure, not a single tracheid is missing. 
1 Voechting, in Hanstein’s Botanische Abhandlungen, iii, p. i, 1875. 
2 Physiologische Pflanzeuanatomie, p. 283. 
