344 BOTANICAL GAZETTE | MAY 
Van TIEGHEM, PH. (1) (et DuLIoT) Recherches comparatives sur lorigine 
es membres endogénes dans les plantes vasculaires. Ann. Sci. Nat. Bot. 
VII. 8 : 1-656. 1888. 
(2) Traite de Botanique. 1891. 
~VinEs, S.H. (1) The systematic position of Isoetes. Ann. Bot. 2: 117-123, 
; 223-224. 1888-9. 
(2). A text-book of botany. 1895. 
EXPLANATION OF PLATES XIII-XX. 
The drawings, except fig. z, have been made with the aid of a camera 
lucida, and all have been reduced by photography to two fifths of their origi- 
nal size. Both in the text and in the explanation of the plates, the terms 
transverse, longitudinal, and tangential, when used to describe sections of the 
ligule and the sporangium are to be understood as indicating the planes in 
which the sporophylls were sectioned. 
Fic. 1. Base of microsporophyll, inner face showing the sporangium (s), 
the velum (v), and the ligule (7). x 4. 
Fig. 2. Radial longitudinal section of base of sporophyll; s, v, 4, aS in fig. 
ta: he 
F1G. 3. Longitudinal section of apex of a small plant. x 48. 
Fic. 4. Longitudinal section of apex of a larger plant; +x, the tracheids, 
Pp, the prismatic layer, ¢, the leaf traces, #, the cambium (semidiagrammatic). 
x 48. 
Fic. 5. Part of the prismatic ring as seen in transverse section of the 
stem ; x, 2, ¢,m, as in fig. 4. X 160. 
Fig. 6. Cortical cells from the neighborhood of the cambium. X 240. 
Fic. 7. Cortical cells from the outer region of stem. X 240. 
Fic. 8. Longitudinal section of a number of young sporophylls ; the sp 
rangia are indicated by the dotted outlines. x 48. 
1G. 9. Cross section of a young leaf above the ligule. X 300. : 
Fig. 10. Cross section of a young leaf more advanced than that shown In 
Jig. 9; the position of the future air chambers is shown by the groups of nearly 
empty cells ; the small circles of figs. g and so indicate the side towards the 
axis of the plant. x 300. 
Fic. 11. Part of a longitudinal section of a leaf more advanced than that 
of fig. 10, showing origin of the air cavities; , the phloem, x, the xylem. 
X 300. ; 
Figs. 12-13. Transverse section of leaf with the vesicular cell from which 
the ligule originates. X 300 
Fic. 14. First division of the ligule, sectioned in plane a—@ of fig. 15: 
499. : 
Fig: 15. First division of the ligule. seen in radial longitudinal section. 
X 490. : 
