4i 6 Hill and Freeman. — The Root-Structure 
himself chiefly to the origin, &c., of the roots and the characters 
presented by their bundle-sheath in species of Tamus and 
Dioscorea. Further, he confirms Treub’s 1 statements regard- 
ing the differentiation of the root-apex of Tamus communis , 
and disagrees with those of Janczewski. 
Anatomy of the large spine-bearing roots. 
These roots attain a diameter of 7 cm. and, as regards their 
structure, conform to the general monocotyledonous type. 
There are, however, certain interesting features exhibited 
which render a brief account of their structure not altogether 
out of place. The apex is somewhat blunt, and is made up 
of an enormous number of very small cells. Inasmuch as our 
material contained but one good and one indifferent apex, 
it was not possible unfortunately to investigate thoroughly 
the apical differentiation ; however, it appears most probable 
that there is, in this plant, no definite calyptrogen layer as 
has already been asserted by Treub *, and confirmed by 
Bucherer 2 , to be the case in the Dioscoreaceae among other 
Natural Orders. 
From a series of transverse sections through the apex it 
may be seen that the central cylinder is of normal diameter, 
and before either the phloem or xylem is differentiated 
a number of canals or vessels are formed in the more central 
regions, roughly arranged in a circle within the zone which 
eventually will be occupied by the phloem and xylem. The 
development of these vessels is extremely remarkable and 
quite dissimilar to what obtains in other plants as far as is 
indicated by existing accounts. They are produced not 
merely by the obliteration of the end-walls of elements 
situated one above the other, but also by the breaking down 
of the lateral walls of contiguous cells in a transverse plane. 
It is not suggested, however, that these structures are formed 
wholly by such a lateral fusion of elements ; for tracing them 
downwards from the apex it is found that they originate as 
1 Treub : Le meristeme primitif de la racine dans les Monocotyl^dones. Leiden, 
1876. 
2 Loc. cit. 
