3 66 Chandler . — On the Arrangement of the Vascular Strands 
is surprisingly scanty, and there can be no doubt that it is just such know- 
ledge which is required at the present time, if the different views which still 
exist upon the ‘ stelar ’ question are to be successfully harmonized. 
It was in the hope of making a contribution — necessarily a small one — 
to such a knowledge that the present work was undertaken. Nearly twenty 
ferns have been examined, mostly belonging to Polypodiaceae, a family 
which will doubtless prove of considerable interest in connexion with 
vascular questions, not only on account of its numerical richness in species, 
but also on account of the great variety of forms occurring within its 
boundaries. 
The majority of the plants examined were obtained, through the 
kindness of Prof. Farmer, from Messrs. James Hill and Son, of Edmonton, 
who afforded the writer every facility for gathering plants of the different 
ages required. 
The methods employed in the investigation were generally of a very 
simple character. Whenever possible, the plants were embedded in paraffin 
and serial sections obtained in the usual way. In some cases, however, 
owing to the presence of sclerenchyma, the celloidin method was resorted 
to, and occasionally, when even this was impossible, the ferns were cut 
by hand. 
The sections were always double-stained with safifranin and haematoxy- 
lene. The well-known method of lightly staining with haematoxylene, 
and subsequently ‘ blueing ’ with ammonia, proved of great value for the 
differentiation of sieve-tubes, especially in very young plants. 
Doodia aspera, R. Br 1 . 
The primary root of this plant is of the diarch type so general among 
the ferns. In the transitional region the xylem plate, by the development 
of tracheides upon its sides, becomes oval and finally more or less circular 
in section, and, at the same time, the phloem is gradually differentiated as 
a continuous sheath surrounding the solid xylem rod (Fig. 197). At 
a slightly higher level, two or three parenchyma cells appear in the centre 
of the xylem (Fig. 198), quickly followed by one or two well-marked sieve- 
tubes (Fig. 199). The early appearance of internal sieve-tubes is a point 
of some interest, since it indicates that almost from its very commencement 
the primary pith is, in reality, phloem ; in other words, it is vascular, as 
opposed to non- vascular tissue. This point, however, will be referred 
to later. 
Just before the first leaf-trace is given off, the sieve-tubes increase to 
about four or five in number, taking up a central position in the internal 
1 The nomenclature adopted throughout is that of Hooker’s * Synopsis Filicum,’ except when 
otherwise stated. 
