IN LEAVES OF GYMNOSPERMOUS PLANTS. 121 
of the centrifugal, but a great development, on the contrary, of 
the centripetal xylem. Here also could be distinctly seen a 
transition between the elements nearest the protoxylem, which 
were quite small, and other tracheides, of great diameter and 
with bordered pits on their transverse walls, which occurred 
scattered in the ground-tissue, often at a considerable distanee 
from the bundle. It was interesting to see how some of these 
tracheides extended round towards the phloem. 
Fig. 2. 
Transverse section of vascular bundle from the upper part of the cotyledon of 
Cycas revoluta, ph-phloem; pxr=protoxylem ; 2! —centripetal xylem. 
In the leaves of some of those Coniferm which approach 
nearest to Gingko, such as Cephalotazus and Taxus, Y observed 
trache ides on the ventral side of the protoxylem, whicb, by their 
othe and general character, may be considered as equivalent 
extender petal xylem in Gingko and Cycas. After a rather 
leaves of beens I came upon similar instances in the 
Collat; ammara, Araucaria, Widdringtonia, and Pinus. 
town ite these facts with the structure as we have long 
Cyeads o. the vascular bundles of the leaves of Conifers and 
found tee > at appears to me that there is a clue to be 
his tissue e ongin of the transfusion-tissue in these plants. 
Gingko is cle een m the cotyledonary bundles of Cycas and 
of the tent carly an extension, towards the sides of the bundle, 
unlimited “petal xylem of the latter. It is the successive, 
tissue which ag Petal development of the tracheides of this 
tually culmi À ords, as it were, the first start which has even- 
nafasin S m more modern plants, in the characteristic 
the vascular " at the side of, or in various positions around, 
faves is not undle. The transfusion-tissue, e. gq. of Coniferous 
> 48 some have supposed, a distinctly new tissue 
