in the Root and Stem of Dicotyledons . 261 
The physiological importance of bicollaterality cannot be 
fully estimated until the general question of the functions of 
the phloem has been finally determined, but it is undoubtedly 
great. The sheltering of a portion, often the larger portion, 
of the delicate phloem within the woody cylinder is an obvious 
advantage, as is also the fuller utilization of the pith-area and 
consequent concentration of the tissues generally. It is prob- 
able also, that the pith-cells themselves may be able to dis- 
charge both storing and conducting functions more efficiently 
when brought into direct relation with the phloem and its 
proteid contents. 
All such speculations are of necessity premature, but in the 
mean time the due consideration of these modified arrange- 
ments may guard us against erroneous views of the functions of 
the phloem, which might be entertained, if we limited our atten- 
tion to so-called normal structure. To this point we shall return. 
The primary object of our work was to investigate the 
structure of the root in plants, which have bicollateral bundles 
in the stem and its appendages. Our observation of medul- 
lary phloem in the root of Strychnos 1 rendered it probable, 
that in other plants a similar continuity of structure between 
root and shoot might be traced. In order to estimate the 
significance of any anatomical character it is evidently 
necessary to know, whether it extends throughout the plant 
or is limited to special regions. As regards the more 
modified dicotyledons, however, our knowledge of their 
characteristic structure is often confined to the subaerial 
organs. And if, as we fully expected to find, medullary 
phloem as such, proved in many cases to be absent from the 
root, it was still desirable to trace its course in the transi- 
tional region, and to see whether it ended blindly or became 
in any way continuous with the normal phloem of the root. 
This point has been very little attended to by anatomists. 
Gerard traced the course of the bundles from root to stem in 
two Solanaceous plants and in Cucurbita. He found that the 
1 On the Anatomy and Histogeny of Strychnos , Annals of Botany, vol. III. 
p. 291, 1889. 
