Seedling Structure of Gymnosperms. II. 191 
states that three are generally present. Their structure resembles many 
of the Cupressineae ; the amount of transfusion tissue is very small, and 
there may be made out, towards the bases of the seed-leaves, a few xylem 
elements situated in a centripetal position. Resin ducts are absent. 
The seed-leaves form a short but fairly well-marked cotyledonary tube, 
and in this region the bundle of each becomes somewhat tangentially 
elongated, an arrangement which is retained during the inward passage. 
After the central region of the hypocotyl has been reached, each trace splits 
into two halves, the bifurcation generally appearing first in the phloem. 
Each half-bundle then rotates around the protoxylem which acts, as it were, 
as the pivot. The wood is thus exposed, and the protoxylem takes up its 
exarch position, in some instances very gradually. The opposing groups of 
phloem elements effect a junction so that a triarch root-structure obtains. 
These changes agree with the brief description given by Dangeard h 
Tsnga diversifolia , Mast., as far as can be ascertained from seedlings 
having much secondary thickening, does not differ in any essential feature 
from T. canadensis. 
Abies. 
The structure of the cotyledons calls for but little comment ; mention 
need only be made of three features. In Abies sibirica , A. Veitckii , A. 
balsamea , A. amabilis , and A. magnifica var. Shastensis , each seed-leaf has 
two resin ducts situated in each corner towards the dorsal surface ; trans- 
fusion tracheides also are present in varying amounts ; and, finally, a cap of 
broad, elongated, thin-walled elements abuts directly on to the dorsal 
surface of the phloem. 
Abies pectinata appears to be somewhat abnormal, for the seed-leaves 
have no resin ducts, and transfusion tissue has not been observed. 
In all the species examined each cotyledon had a single bundle which 
retained its endarch character until the central region of the hypocotyl had 
been reached. 
Abies sibirica has three or four cotyledons. The examination of a 
specimen with the former number showed the transition to be identical with 
what obtains in Tsnga canadensis , and resulted in the formation of a triarch 
root-structure. A seedling (Series B) which had four cotyledons behaved 
somewhat differently, and requires some description. All the seed-leaves 
were quite free for the greater part of their length, but towards the basal 
region two of them were fused together, so that a transverse section at this 
level had the appearance illustrated in the first figure of Diagram 1. The 
four bundles of the seed-leaves retained their identity within the hypocotyle- 
donary axis for some time, and were surrounded by a practically closed 
ring formed by the fusion of the fibrous elements of the four phloem masses. 
1 Dangeard, loc. cit. 
