18 
Isabel Browne. 
As a rule the transition from the bundle with two metaxylem 
groups to the type of bundle characteristic of the cone occurs a 
little above the annulus. In E. giganteumf presumably correlated 
with the vascularization of the annulus, the change occurs a little 
below the insertion of the annulus; so that in this species the 
bundles just below the annulus much resemble the bundles of the 
internode of the cone (cf. Text-Fig. 6 a, of a bundle in this region 
with Text-Fig. 4 b). Usually the lateral bands of metaxylem 
become united with any persistent tracheides of the carinal group, 
and when this linking up is completed we get for a time a distri¬ 
bution of the xylem of the bundles recalling strikingly that found 
in the bundles represented in Text-Fig. 2 a and b. Text-Fig. 6 c 
shows a phase in this process in a bundle of E. arveuse. Here one 
of the lateral groups of metaxylem has spread almost as far as the 
edge of the carinal canal, while the other has hardly increased in 
size or changed in outline. Text-Fig. 6 b, is of a bundle of 
E. giganteum, a little way below the insertion of the annulus, before 
the xylem has assumed the form characteristic of the internodal 
bundles of the cone. 
We may now consider very briefly the structure of the 
bundles in the internode of the rhizome. So far as 1 have been 
able to ascertain, there is only one case recorded from the rhizomes 
of existing Equiseta in which the lateral groups of metaxylem show 
any approach to the carinal group of tracheides. Such an 
approach occurs, according to Queva, in the rhizomes of E. litorale 
(14, p. 30), where the lateral metaxylem is only separated by a 
single cell from the protoxylem adhering to the carinal canal. It 
is by no means surprising that examples of bundles in which the 
lateral metaxylem is sufficiently well-developed to approach close 
to or to come into contact with the protoxylem are rare in the 
rhizome; for Queva has shown that the metaxylem is generally 
less well developed in this region. Indeed, according to him, it 
may sometimes be completely wanting from the rhizomes of 
E. maximum and E. limosum (14, p. 30). Milde’s figure of a part 
of the rhizome of E. pratense shows three bundles, one without any 
lateral metaxylem and two with a single metaxylem-tracheide on 
one side and none on the other (12, pi. VII, Fig. 9). Milde also 
figures a bundle without lateral metaxylem from the rhizome of 
E, maximum (12, PI. IV, Fig. 1), though his figures of other 
bundles of the rhizome of this species show the lateral metaxylem 
1 The structure of this cone is more fully described in a paper soon to 
be published in the Annals of Botany. 
