68o Browne.— Contributions to our Knowledge of the 
neighbouring strands a mesh is very nearly closed at the level of a whorl, 
and when a trace departs from the edge or very near the edge of one of 
these strands, it may alternate more or less accurately with the traces of the 
whorl below, despite the persistence of the mesh through the node. When 
a strand pursues an isolated course through several nodes (i. e. when the 
parenchymatous meshes on both sides of it extend upwards through several 
nodes and internodes) the traces which it gives off, whether lateral or 
median, are necessarily superposed, though not always accurately so. For 
when the strand is markedly wider than the traces, successive traces may 
depart from portions of the strand not in the same vertical line ; the traces 
may, however, be accurately superposed, and when the strand is hardly, if 
at all, wider than the traces, the superposition is necessarily accurate. The 
giving off of superposed traces from an isolated strand seems to be an effect 
of reduction of the xylem, whereby neither of the meshes bordering the 
strand is closed at the nodes ; it is, therefore, natural that this form of 
superposition of the traces should be commonest in E. limosum , especially 
in Cone B : but it is common, too, in E. palustre, and occurs, though rarely, 
in E. arvense (e. g. the ninth and tenth traces of the second whorl of Cone C 
are given off from isolated strands, and are superposed respectively to the tenth 
and eleventh traces of the whorl below ; and the tenth and eleventh traces 
of the fifth whorl of Cone C are borne by isolated strands, and are super- 
posed to the tenth and eleventh traces of the whorl below). 
In E. Ihnosum , though the xylem at the nodes is in excess of that in 
the internodes, it is only rarely sufficient to close a mesh before the departure 
of the trace at that node, i. e. to unite two trace-bearing strands, as, for 
instance, the strands giving off the seventh and eighth traces of the third 
whorl of Cone A are united. More often the strand, though relatively 
wide, is not wide enough to come into contact with its neighbours ; when 
a trace departs from the median portion of such a strand a parenchymatous 
mesh appears a little way above it so that the strand appears to fork just 
above the node. When two neighbouring strands branch in this way their 
adjacent branches diverge obliquely and fuse a little higher up to form the 
trace-bearing strand of the next internode (Text-fig. 7, B) ; we thus get 
a regular alternation such as obtains in the vegetative stem. But in the 
latter, generally in the cone of E. arvense , and frequently in the cone of 
E. palnstre , there is no need for this fusion to constitute fresh strands alter- 
nating with those of the internode below, for the strands are, as a rule, 
laterally in contact with one another at the nodes at or before the departure 
of the traces, and by the appearance of parenchymatous meshes above the 
latter, strands arise alternating regularly with those of the internode below 
(Text-fig. 7, a). In both these cases, represented respectively by Text- 
fig. 7, A and B, we get a regular alternation of strands at the nodes ; but 
in the form of alternation illustrated in Text-fig. 7,B, rather less xylem is 
