538 Bower .—( 9/2 the Primary Xylem , and the 
with the cortex.’ This was probably the first example of encroachment of 
the cortex upon the stele to be observed or described in vascular plants. 
The same author further pointed out that between the invaginated endo- 
dermis and the internal margin of the wood one or two layers of 
parenchyma intervene, which are continuous at their margins with the 
pericycle. So, according to his view, the pericycle is invaginated like the 
endodermis. Further up the axis the internal endodermis separates com¬ 
pletely from the external, and henceforth there are two distinct layers of 
endodermis, one external, the other internal. This structure is continued 
upwards, but above the fourth leaf the internal endodermal characters were 
gradually lost, and in the adult plant there is only a single endodermis, 
i. e. the external. An internal endodermis was not found in B. ternatum , 
virginianum , or daucifolium , but it was clearly seen in B. boreale. 
There were no illustrations of the data thus described by Van Tieghem, 
but subsequently M. G. Poirault, to whom the observation appears to have 
been in the first instance due, delineated the internal endodermis for 
B . Lunaria , and also for Ophioglossum Bergianum , in both cases finding it 
present only at the base of the plant. 1 An internal endodermis has since 
been found, and described in the old stocks of Helminthostachys zeylanica, 2 
A current view which has been based upon these descriptions is that the 
pith of the Ophioglossaceae is to be ranked as intrusive cortex, with a lining 
of endodermis and pericycle. In the case of Botrychium the primary wood 
would then lie, such as it is, between the parenchyma which Van Tieghem 
described as internal pericycle and the zone of secondary wood. 
It seemed desirable, in view of the advances in stelar investigation in 
other plants, to look again into the facts relating to the Ophioglossaceous 
stele. There is a general opinion that here, as elsewhere, the stelar con¬ 
dition has been ultimately derived from the solid protostele. Van Tieghem 
describes this structure for Ophioglossum vulgatum (loc. cit., p. 405) and 
Botrychium Ltinaria (loc. cit., p. 407). In Ophioglossum vidgatum Van 
Tieghem states that ‘ in the whole region below the first leaf there is 
a central cylinder which is slender and without pith’ (loc. cit., p. 405). 
I do not find this to be constant in plants sprung from adventitious buds 
on the roots. A pith may be present in these from the very first. The same 
medullated condition is found to be the case in some specimens of O. reti- 
culatum , but others show a solid xylem up to a point immediately below the 
departure of the first leaf-trace. In O. palmatum such young plants as were 
observed were medullated from the first (PL XLV, T ig. 1). It appears, there¬ 
fore, that variability exists within the genus Ophioglossum in respect of the 
medullation of the individual in the young state. There is some reason 
for believing that the existence or non-existence of a pith from the first 
1 Poirault, Ann. Sci. Nat., 1893, pp. 169, 170. 
2 Farmer and Freeman, Annals of Botany, vol. xiii, p. 421, PI. XXII, Fig. 11. 
