THE EMBRYOLOGY OF CARPINUS BETULUS. 13 
secure the safe passage of the pollen-tube from the stylar region down the raphe, and in 
both its entry into the nucellus is facilitated by the obliquity of the chalaza. 
In both genera (not only in Casuarina, as is implied in Engler's ‘Syllabus der 
Pflanzenfamilien,’ 1903) a large number of perfect embryo-sacs may be formed, and in 
Carpinus more than one egg-cell may be fertilized. 
In the various stages of the development of the sporogenous tissue and of the embryo- 
sacs, in the early degeneration of the antipodals, the formation of the emen, the long 
rest of the egg-cell before segmentation (while the endosperm is rapidlydeveloping), 
and in the development of tracheides around the megaspores, we have such a consensus" 
of characters as leaves us little to separate the two genera on embryological grounds. 
On the whole, the most important characters in which Casuarina differs from Carpinus 
are its switch-like habit of growth and its phyllotaxis. These, when combined with some 
minor differences in floral structure and ia embryology, may suffice as grounds for 
forming a distinct group within the family Betulacec of equivalent rank with Corylez. 
This family would then include the three subfamilies Corylez, Casuarinex, and Betulew. 
Such a classification would emphasize the close genetic aflinity between Carpinus and 
Casuarina, and the term Verticillate, as used by Engler in the ‘ Syllabus’ and * Das 
Pflanzenreich,’ could then be dispensed with altogether. 
BIBLIOGRAPHY. 
1. “ Zur Entwickelungsgeschichte der Chalazogamen Corylus Avellana, L.” Von Sergius Nawaschin, 
Prof. der Botanik an der Universitit Kiew. Bulletin de l'Académie Impériale des Sciences de 
St. Pétersbourg, 5* série, vol. x. 1899, pp. 375-391, tt. 1, 2. 
2. * Ueber die gemeine Birke." Von S. Nawaschin. Mémoires de l'Acad. Imp. des Sciences de 
St. Pétersbourg, xlii. n. 12 (1894). 
3. * Contributions to the Embryology of the Amentiferz.— Part L" By M. Benson, D.Sc. Transac- 
tions of the Linnean Society, ser. 2, Botany, vol. iii. (Feb. 1894) pp. 409-124, pls. 67-72. — 
EXPLANATION OF PLATE 6. 
Fig. 1. Shows the course of the pollen-tube, p.t., in the integument, chalaza, ch., and fully developed - — 
embryo-sacs, e.s., of an ovule. in., inner integument; ez. outer integument; n., nucellus; 
e.c., egg-cell ; d.n., definitive nucleus ; 7., raphe. -o o o 
2. Diagram from a series of sections through an immature nucellus. pe pollen-tube, Pt, is : 
coiled repeatedly round the outside of the young embryo-sacs, ¢.8.—A curious feature in the : - 
ovules of the tree from which this specimen came is that the cca, c., invariably tended to — 
turn away from the chalaza, ch., and bore through the distal wall of the nucellus, n. One 
ovule from this tree contained two nucelli. 
