and Histogeny of Strychnos . 279 
the phloem-islands, had already been done before we became 
acquainted with HeraiFs paper, so that our points of agree- 
ment with him afford an independent confirmation of his 
statements. 
General Structure of Stem. 
Before tracing the development in detail, it will be useful 
to give a short description of the structure of a well-developed 
stem. If a transverse section of an internode of Strychnos 
mix vomica , L,, not less than 5 mm. in diameter 1 , be ex- 
amined, the following structure is observed. On the outside is 
an external periderm, consisting of several layers of cork, 
with scanty phelloderm. Within this is the parenchymatous 
cortex, of no great thickness, and then a dense two-layered 
ring of very sclerotic cells. This immediately surrounds the 
radially arranged bast-parenchyma. In its outer region the 
small groups of primary phloem may still be recognized here 
and there. Next comes the cambium, and within this the 
broad zone of wood, occupying much the greater part of 
the whole area. Scattered about in the wood, and arranged 
irregularly in three or four concentric rings, we find the 
phloem-islands, roundish groups of soft bast separated from 
one another by broad tracts of the continuous mass of wood. 
At the inner boundary of the wood lies the ring of medullary 
phloem-groups, intruding into the pith. They are usually 
about twelve in number, and are of almost the same size as the 
phloem-islands in the wood. The pith itself is rather thick- 
walled, and in our specimens is of uniform structure through- 
out, containing abundant starch. One very conspicuous point 
is, that all the medullary phloem-groups, and all the more 
deeply-seated islands show great masses of crushed and ob- 
literated tissue, and it is at once seen that in the phloem- 
islands of the wood the obliterated tissue invariably lies on 
the outer side, while in the medullary groups it is as constantly 
1 The stem in question was at least five years old, probably more. We were 
not able, in hot-house grown plants, to distinguish the annual rings with certainty 
beyond the second year. 
