Studies in the morphology of spore-producing members.—Equisetineæ and Lycopodineæ

Abstract

Observations of Hofmeister stand, in their broad outlines, as the foundation of morphology of archegoniate plants. It will be assumed that readers will accept in ain the homologies which, on the basis of those observations, he recognized in the corresponding parts of the Bryophyta, Vascular Cryptogams, and Gymno- ; it will also be assumed that, whatever may have been the circumstances led to it, antithetic alternation was brought about by elaboration of the zygote to form a new generation (the sporophyte) interpolated between successive ophytes, and that the neutral generation is not in any sense the result of cation or metamorphosis of the sexual, but a new product having a distinct genetic history of its own. Those who accept this view will keep distinct in ninds the sexual generation or gametophyte on the one hand, and the neutral ition or sporophyte on the other, whatever their variations, either in relative Physiological dependence; and they will recognize that no homologies are admitted between them or their parts. Clear conceptions on these points are itely essential, if there is to be real progress in comparative morphology; though tody of either generation may shed side-lights upon the problems relating to the it e two alternating generations.must be treated apart, so long as the main Hofmeister continue to be accepted. The assumption above made as to the origin of antithetic alternation is based upon Inparison of living plants, which leads to the conclusion that, of the two, generations, the sexual generation (the oophyte or gametophyte) was the: tilat subsequently a neutral (the sporophyte) was produced as a stage interpolated between the successive sexual generations; and that this new Produced, not by mere modification of the oophyte, or of a part of it, but by amplification of the product of sexuality— the zygote; by its sub-division into numerous cells the effect of a single sexual process is distributed over the parts produced these parts, when isolated, may be styled the spores , or, to distinguish them from other unicellular organs of propagation, they are designated by the special term “ carpospores ” Further comparison of living forms leads to the conclusion that the followed upon the increasing size of the sporophyte a progressive sterilization of tissues, so that only a part of those tissues continued to be sporogenous; this most readily illustrated by reference to the Bryophyta (see below, p. 485, &c.), a series plants in which progressive sterilization of the tissues of the sporophyte appears have been closely connected with its increasing size and structural complexity. The series is, however, characterized by the simple external form of the sporophyte, an by the further fact that the sporogenous tissue of each individual sporophyte normally a continuous mass; accordingly, the recognition of the progressive steriliz; tion is in them comparatively easy.