11 
Plate CXITI. 
Fig. 14. The rhizome with the leaves and an inflorescence of Diclytra Cucullaria 
Natural size. 
Fig. 15. Part of the same, showing the petioles of two normal leaves (L), and the 
base of the inflorescence, (I). The scale-like leaves have been removed, and 
in their axils are clusters of small tuber-shaped leaves to be seen. 
Fig. 16. One of these clusters from the axil of a scale-like leaf. 
Fig. 17. A tuber-shaped leaf, showing the small rudimentary toothed blade. 
Fig. 18. A small specimen, developed from a tuber-shaped leaf, showing the tuber- 
ous base of a leaf, of which the petiole has faded, and a short axis, carrying a 
root, one scale-like and one normal leaf. 3 x natural size. 
Fig. r9. A similar plant with three scale-like leaves, surrounding the normal one. 
3 x natural size. 
Fig. 20. A similar plant, of which the scale-like leaves have dropped, and where 
the base of the normal leaf shows the tuberous swelling. 3 x natural size. 
Fig 21. The base of a normal leaf, in the axil of which clusters of small tuber-like 
leaves are to be seen, 
Fig. 22. Part of the rhizome of a specimen collected in August, showing a bud sur- 
rounded by tuber-like leaves. 
Fig. 23. One of these tuber-like leaves at the same time, showing the cavity at the 
base, in which a bud is to be seen. 
Fig. 24. The axillary bud, taken out from the cavity, showing two very young 
leaves. 
Fig. 25. A mature specimen of Avigia Dandelion, showing the leafy rosette and the 
rhizome, natural size. 
Fig. 26, The rhizome of another specimen, where a stolon has developed a leafy 
rosette, not being preceded by any tuber, as in Fig. 25. Natural Size. 
U.S. National Museum, Washington, D.C. Aug. 1890. 
Recent Contributions to the Literature of the Diatomacez. 
La Structure de la Valve des Diatomees. Dr. Henri Van Heurck. 
(Annales de la Societé Belge de Microscopie. xiii. 1890). 
By the aid of Zeiss’s new apochromatic one-tenth inch ob- 
jective of 1.63 N. A., using monochromatic sunlight, compensat- 
ing eye-piece and condenser 1.6 N. A., Dr. Van Heurck has 
produced a series of photographs which go far towards clearing 
up our ideas of the structure of the diatom valve. From his re- 
searches he derives the following conclusions : 
1. Diatom valves consist of two membranes or thin films, and 
of an intermediate layer, the latter being pierced with openings. 
The outer membrane is very delicate. It is supposed that these 
membranes are sufficiently permeable to allow circulation by en- 
dosmose, though they have no real openings) during the life of 
the diatom, 
