[KIRSCH] CERTAIN STRUCTURES IN THE PTERIDOPHYTES 369 
Besides the formation of a schizogenous space at this stage, a 
secondary phenomen is observable in some cases. In the region of the 
protoxylem there is an abundance of delicate, thin-walled, wood paren- 
chyma, and some of the cells of this tissue which lie in the line of the 
schizogenous break become ruptured and form a space continuous with 
the other, but containing protoplasmic remains. In this manner there 
is formed a lysigenous cavity confluent with the schizogenous one. 
Coming toward the base of the bud, the breaks in the protoxylem 
become more frequent, 1.e. are found in more bundles in transverse sec- 
tion, are much larger, and take on the nature of canals. Moreover, in 
one or two places about 2 cm. from the base, some of the parenchyma 
cells bordering the canal were observed to bulge out, and this is the first 
indication of thylose development. 
At the base of the bud the secondary xylem shows very thick walls 
which are highly lignified, and the T-shaped bands of sclerenchyma, 
which become evident near the tip of the bud and proceed from there 
to the base running between the bundles, are strongly marked. In this 
region the breaks in the protoxylem are found mostly in bundles of com- 
paratively large size; the lacunæ, however, are very small and frequently 
show thylosal growths. 
In the smaller buds the breaks in the protoxylem were less evident, 
and showed a purely schizogenous origin, i.e. the parenchyma cells were 
not ruptured (Fig. 1 A). This is no doubt due to the less rapid growth 
of the tissues as a whole. Thus in this case the force would be sufficient 
to tear the protoxylem cells away from each other, but not enough to 
rupture the wood-parenchyma cells. Most of the bundles in these buds 
showed the protoxylem intact and this was to be expected from what 
was found in other cases to be mentioned below. 
The bud is an underground structure and is that part of the re- 
sultant stipe which remains in the substratum. When growth begins in 
the spring, the bud elonvates by apical growth, the tip thus rising above 
the soil. The continued elongation of the tip gives rise to the stipe, | 
which is surmounted by the pinnæ as they gradually unfold. In the 
following descriptions of the structures in the stipe, only that part of 
the stipe which is above ground, will be dealt with, the subterranean 
portion being dealt with separately. Thus, by the base of the stipe, will 
be meant that part cut off at a level with the surface of the substratum ; 
the tip of the stipe being just at the juncture of the stipe proper with 
the main pinne. 
The first stipes to be described were cut on May 29th, 1899, when 
growth was still proceeding rapidly, the tissues being in a formative 
state. 
see, Ve. 1907S. 28: 
