Apogamy in Ferns . 197 
meiotic nuclei, and the case of Lastrea pseudo-mas var. cristata apospora 
shows that the converse is also possible. 
The general conclusion to be drawn from this somewhat lengthy 
discussion, on the relation between the periodic reduction in the number of 
the chromosomes and the alternation of generations, is that no necessary 
correlation exists between the two phenomena, and therefore the problem of 
alternation and its nature must be settled by an appeal to evidence other 
than that derived from the facts of meiosis. That alternation is normally 
associated with meiosis on the one hand and with zygosis on the other 
no one will dispute so far as the Archegoniatae are concerned. But in the 
absence of all proof of the existence of a necessary and causal connexion, 
or rather in the face of direct evidence to the contrary, it is scarcely to be 
wondered at that the presumed correlation should often be broken as 
ontogeny becomes more complex ; and thus the way is paved for the 
appearance of exceptions which, so long as they are of rare occurrence, 
are often regarded as monstrosities or abnormalities ; but when they become 
common they are rather to be looked upon as proofs of current physiological 
instability than as keys for the immediate solution of problems in mor- 
phology or phylogeny. 
EXPLANATIONS OF FIGURES IN PLATES XVI-XX. 
Illustrating Professor Farmer and Miss Digby’s paper on Apospory and Apogamy in Ferns. 
[The nuclei have all been drawn with the camera to the same magnification (x 1500) 3 mm. 
Horn. Imm. Zeiss. Oc. 18, except Fig. 32, which was drawn under 2 mm. Horn. Imm. Zeiss. Oc. 18 
(X 2250).] 
PLATE XVI. 
Athyrium Filix-foemina var. clarissima. 
Fig. 1. Sporangium (young) before the archesporium is delimited. 
Fig. 2. Sporangium with apical prothallial growth (/). 
Fig. 3. Prothallial growth, 4-celled. 
Fig. 4. Abortive sporangium with three prothallial outgrowths. 
Fig. 5. Multicellular prothallium from apex of the abortive sporangium ; the archesporial tissue 
(a) can be distinguished. 
Fig. 6. Abortive sporangium with four prothallial outgrowths. 
Fig. 7. Abortive sporangium with older prothallium. 
Fig. 8. First prothallial cell in division, nucleus in equatorial plate stage. The cells below 
the one in division belong to the sporangium. 
Fig. 9. Nucleus from wall of young sporangium in equatorial plate stage, for comparison with 
the preceding figure. 
Figs. 10, 11, 12. Nuclei of young prothallial cells, nu , nucleoli, x 1500. 
Fig. 13. Prothallial nucleus in early prophase of mitosis, x 1500. 
