5 1 6 Boodle . — On the Occurrence of 
of the stem. They are to be regarded as reduced secondary xylem, and 
they are present in the aerial as well as subterranean stem. 
There is no definite cambial layer, but radial arrangement among the 
parenchyma and tracheides is often found, and parenchymatous rays opposite 
the protoxylems are sometimes present. 
The secondary tracheides are scalariform or irregularly pitted, and often 
have a sinuous course. 
The presence of secondary tracheides around a triarch primary xylem, 
such as occurs in some parts of the stem, gives a close approximation to the 
structure of the stem of Sphenophyllum . 
In the lower region of the aerial stem a few cases of apparent mesarch 
structure were observed. If this should be verified, an important distinction 
between P silo turn and Tmesipteris would break down, and a further agree- 
ment between the aerial stem of Psilotum and the axis of Cheirostrobus 
(already rather striking) would be established. 
Thus the new facts derived from a study of the vegetative anatomy 
strengthen the hypothesis of the affinity of the Psilotaceae with the 
Sphenophyllales. This view, put forward by Scott and adopted by Thomas 
and Bower, was founded partly on the vegetative anatomy, but more 
especially on the characters of the sporophylls. 
The production of secondary tracheides in subterranean parts is 
probably dependent on the development of aerial shoots, and appears to 
be due to a basipetal stimulus from the latter. 
In conclusion I wish to express my thanks to Dr. D. H. Scott, F.R.S., 
for valuable suggestions and criticism and for information regarding 
Sphenophylleae. 
List of Works referred to. 
Bertrand (’81) : Recherches sur les Tmesipterid^es, Archives botaniques du Nord de la France, 
tome i, p. 252. 
Boodle (’99) : On some points in the anatomy of the Ophioglosseae, Annals of Botany, vol. xiii, 
P- 377- 
Bower (’03) : Studies in the morphology of spore-producing members. No. V. General Com- 
parisons and Conclusion, Phil. Trans. Roy. Soc., Series B, vol. 196, p. 191. 
Brongniart (’37) : Histoire des v^g&aux fossiles, ii. 
Dangeard (’ 91) : M<fm. sur la morphologie et l’anatomie des Tmesipteris , Le Botaniste, 2 0 sdr., 
1890-1891, p. 163. 
De Bary (’77) : Comparative Anatomy of the Phanerogams and Ferns (Engl. Ed., ’84). 
Lignier (’03) : Equis^tales et Sphenophyllales. Leur origine filicineenne commune, Bull. Soc , 
Linneenne de Normandie, 5® serie, 7® vol., p. 93. 
Link (’ 42) : leones selectae anatomico-botanicae, fasc. iv. 
