456 MR. J. R. GREEN ON THE ORGANS OF 
details of the formation of these glands and passages, it will be 
most convenient to take first the second class, the resin-passages 
in the stems and flowers. Their situation in the different parts 
of these has already been described. They are to be found in both 
the thick-leaved shrubby species and in those of more slender 
habit, but are best traced in Hypericum calycinum. Each passage 
in the stem arises independently, a little below the growing- 
point. Their first appearance may be noticed about the same 
time as that of the differentiation of the procambium bundles, 
or perhaps a little later. The fundamental tissue in which they 
arise, two or three layers of cells below the epidermis, is com- 
posed of cells which in cross section are polygonal and in longi- 
tudinal section are oblong, about five times longer than their 
transverse diameter. In the midst of such cells rows of cells 
appear, at first single in eross section, which begin to divide 
differently from their neighbours, while their protoplasm becomes 
more granular and stains more deeply. Soon the single cell is 
found to have divided into two, each of these again into two, and 
then, by irregular divisions, into a larger number of cells, forming 
a strand of tissue, which, in longitudinal section, is seen to consist 
of small oblong cells with very delicate walls and very granular 
contents, the nucleus being well marked in each (Pl. XXXIX. 
figs.1—4and fig. 9). Such a section at this stage generally shows 
about three or, at most, four rows of such cells forming the 
strand. They are about one fourth or one fifth the length of 
the cells of the fundamental tissue which surround them, and 
about half as broad. As the stem in its growth lengthens, the 
differentiation of the strand aecompanies it, and the secreting- 
organ thus follows the elongation. The thickening of the strand 
of cells causes it to press on the cells of the fundamental tissue, 
and hence in its immediate neighbourhood these are smaller and 
somewhat flatter than those which surround it when younger. 
After, by repeated divisions, the cross section of the strand has 
come to consist of about twenty cells, the tissue in its centre 
is found to be somewhat looser than it was when younger 
(fig. 5). Intercellular spaces in the strand are more marked as 
the growth proceeds (fig. 6). In fact, almost all through its 
development, the cells are found not to be in close contact 
throughout. In some sections, when as few as three or four cells 
constitute its thickness, small intercellular spaces may be seen 
at their point of union (figs. 2 and 3). From the time, however, 
