428 PHANEROGAMS. 



the tissue of the nucleus, tilled with food-materials, remains unchanged until the seed 

 is ripe, it is distinguished as the Perisperm ; its food-materials, although lying outside the 

 embryo-sac, are consumed by the embryo during germination ; and the perisperm may 

 then act physiologically as the representative of the endosperm^ The seeds, e.g., of 

 Cannaceae and Piperaceae, contain perisperm. Sometimes the ovule, during the period 

 of its development into a seed, is enveloped from below by a new coating, which usually 

 itself surrounds the tough testa as a soft mantle, and is termed the Aril. Of this* nature 

 is the red pulp which surrounds the hard-shelled seed of the yew ; and the origin is the 

 same of the so-called 'mace' of the nutmeg, the seed oi Myristicafragrans. 



If we now turn our attention to the morphological nature of those structures from 

 w^hich the ovule immediately springs, we find a considerable variety. Only rarely does 

 the orthotropous ovule appear as the prolongation or terminal structure of the floral 

 axis itself, so that the nucleus forms directly the vegetative cone of the latter, as in 

 Taxus and Polygonaceae. It is more usual for the ovule to grow laterally on the 

 floral axis, thus corresponding in position to a leaf, as in Juniperus, Primulaceae, and 

 Compositae. But the most common case is where the ovules spring from undoubted 

 leaves — the carpels— and usually from their margin, like pinnae from the leaf (this is very 

 clear, e.g. in Cycas), more rarely from their upper (or inner) side (as in Butomus, 

 Akebia, Nymphaea, &c.). If the ordinary morphological definitions are applied to these 

 relationships, we should have in the first-named case ovules of an axial nature, or they 

 would be metamorphosed caulomes^; where they spring laterally from the axis, they 

 would have to be considered as metamorphosed entire leaves ; and where they proceed 

 laterally from the margins of carpellary leaves, as metamorphosed pinnae. For those 

 ovules which spring from the surface of carpels there is no clear analogy with any 

 purely vegetative structures {i. e. with any that do not subserve the purpose of fertili- 

 sation) ; though in this case we may be reminded of the sporangia of Lycopodiaceae. It 

 appears, how^ever, possible to regard some ovules, as, for instance, those of Orchideae, as 

 metamorphosed trichomes (like the sporangia of Ferns and Rhizocarps). The ovules, 

 finally, of some Cupressineae, which appear to have an axillary position on the carpels, 

 have not yet been sufficiently investigated with respect to their true relationships. In 

 some cases the morphological interpretation is supported by malformations which not 

 unfrequently occur. Cramer, to whom we are indebted for an admirable investigation 

 of this question, has shown that the ovules of Primulaceae and Compositae, which arise 

 laterally beneath the apex of the axis of the flower, become gradually transformed into 

 entire leaves of the ordinary form ; and that in the same manner the ovules of Delphi- 

 nium, Melilotus, and Daucus, which spring laterally from the margins of the carpellary 

 leaves, may become developed into ordinary parts of the lamina, as laciniae or leaflets. 

 It appears on the other hand significant that nothing of the kind has yet been observed 

 in those ovules which have been interpreted above as metamorphosed portions of the axis 

 or as trichomes. The development not only of normal, but still more plainly that of ab- 

 normal ovules, shows further that a morphological distinction exists between the nucleus 

 on the one hand and the funiculus together with the integuments on the other hand. In 

 those anatropous ovules which may be regarded as metamorphosed leaves or parts of 

 leaves, the nucleus makes its appearance of a new lateral structure inserted on the body 



1 [The endosperm and perisperm are generally both included in English text-books under the 

 term * albumen,' a term vs^hich should by all means be avoided, as conveying the idea of a definite 

 chemical composition, whereas that of the endosperm varies greatly. — Ed.] 



^ Cramer, — Bildungsabweichungen bei einigen wichtigeien Pflanzen-familien, u. die morpholo- 

 gische Bedeutung des Pflanzeneies (Zurich i864\— is inclined to consider all ovules as metamor- 

 phosed leaves or parts of leaves. To this view I have already expressed some hesitation in the first 

 edition of this book ; the description here given, which differs from the earlier one, is derived as 

 much as possible from direct observation. 



