406 Chandler . — On the Arrangement of the Vascular Strands 
in which it was continued through two internodes were noted above), then 
we have a condition of affairs resembling in all essential points the mature 
structure of ferns described by Gwynne-Vaughan as solenostelic 1 . That 
such solenostelic vascular systems have passed through the previously 
described ontogenetic conditions has been shown by Gwynne-Vaughan 
in Alsophila , and by the writer in Dickso7iia. From the solenostelic to the 
dictyostelic type the changes are rapid and obvious. They merely depend 
upon the rates at which the leaf-gaps overlap one another, and the final 
result is the formation of a vascular network of the type familiar to 
every one. 
A group of plants very interesting in this connexion is the Osmun- 
daceae. De Bary 2 and Van Tieghem both recognized the striking 
difference of the vascular organization from the ordinary leptosporangiate 
type, and the latter author, from a study of seedlings, maintains that the 
plant in question possesses, as in the case of Phanerogams, a medullated 
monostele. The Osmundaceae have also received the attention of Leclerc 
du Sablon 3 , and later of Zenetti 4 , Faull 5 , and Seward and Ford 6 . 
The work of Faull is of especial interest, since a type of vascular 
system new to the Osmundaceae was discovered in Osmunda cinnamomea. 
This plant, it will be remembered, possesses an internal endodermis ; 
internal phloem, however, is absent, except occasionally at the ramular 
gaps. The internal endodermis, moreover, is sometimes continuous with 
the external endodermis through the foliar gaps, and generally so through 
the ramular gaps. It follows that at such regions the parenchyma sur- 
rounded by the internal endodermis, and the external ground-parenchyma, 
are put into continuity. The author concludes that the internal and 
external parenchyma are morphologically identical, and from this con- 
clusion there can, perhaps, be little question of dissent ; but the contention 
that the vascular system of O. cinnamomea represents a degenerate 
siphonostelic type is not so convincing. The present writer fully agrees 
with the criticism of Boodle 7 , that the great weakness of Faulls position 
results from a neglect, no doubt compulsory, of the ontogeny of the 
vascular system of the plant concerned. In fact, the whole question 
depends upon how and when the internal endodermis with its included 
ground-parenchyma arises, and this can only be settled by a study of 
young plants. The writer believes that such a study will show that 
the internal endodermis arises as a necessary accompaniment of a typical 
ground-tissue pocket, similar to those described above, and differentiated 
early in the life of the plant. This pocket has, in all probability, 
1 Observations on the anatomy of the Solenostelic Ferns, Annals of Botany, xv. 
2 Loc. cit., p. 319. 3 Loc. cit. 
* Das Leitnngssystem in Stamm von Osmunda regalis. Bot. Zeit., 1895. 
5 Loc. cit. 6 Loc. cit. 
7 Further observations on Schizaea. Annals of Botany, xvii. 
