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926 limitation of the genera proposed in Hooker and Baker's "Synopsis Filicum," that being the arrangement followed in the Handbook, Bentham's "Flora Australiensis," and other colonial floras, and the one acquiesced in by most English systematists. But European pteridologists as a rule accept a much larger number of genera, with a somewhat different sequence. And it must be admitted that Polypodium, Nephrodium, Asplenium, and other genera, as defined in the Synopsis, are for the most part artificial assemblages of species, possessing very diverse characters and relationships. But though it is comparatively easy to separate a group here and there as being undoubtedly worthy of generic rank, it is admittedly a matter of great difficulty to prepare good and natural generic subdivisions for the whole order, and although many attempts have been made not one of them has received a wide acceptance. The most recent classification is that given in Engler and Prantl's "Die Naturlichen Pflanzenfamilien," where the class Filicales is divided into 12 familes and 140 genera, against the 75 genera adopted in the "Synopsis Filicum." The 31 genera of New Zealand ferns are spread out into 42 in the Pflanzenfamilien.

The development of ferns can only be briefly alluded to here. In germination the spore produces a small flattened or rarely filamentous prothallium, usually containing abundant chlorophyll, but without vascular tissue. It becomes quite free from the spore, but is of comparatively short duration. On the under-surface of the prothallium the reproductive organs are formed. The male organs are called antheridia, and consist of minute subglobose bodies each containing numerous motile cells known as spermatozoids, resembling spirally coiled filaments, pointed at one end and bearing numerous cilia. The female organs, or archegonia, are flask-shaped bodies partly sunk in the tissue of the prothallium, each containing a single free cell called the oosphere. Fertilisation is effected by the entrance of spermatozoids into the cavity of the archegonium, and by the fusion of one of them with the oosphere. The oosphere then gradually develops into a young plant.

Since the publication of the Handbook several pamphlets or books dealing with the ferns of the colony have appeared. The most important of these are Mr. G. M. Thomson's "Ferns and Fern Allies of New Zealand" and Mr. H. C. Field's "Ferns of New Zealand." Both of these contain much interesting and valuable information, and should be consulted by all students of the order.