ANGIOSPERMS. ^"jr^ 



B. Ovules produced on the Axis and springing from the prolongation of the 

 floral axis within the ovary, the carpels themselves being sterile; these may 

 be either — 



4. Lateral, when they stand beside or below the apex of the floral axis, 



which either rises as a columella and bears a number of ovules (as 

 in Fig. 392), or is arrested in its development, so that the single 

 ovule formed appears terminal (as in Fig. 393); or, 



5. Terminal, when the apex of the floral axis itself becomes the nucellus 



(as in Fig. 391, and in Piperacese, Naias, Typha, &c.). 



To which of these classes the ovules belong in any given plant must be decided 

 in each separate case ; the position on the margin of the carpels is by far the most 

 common among Angiosperms, both the superficial and the axial position belonging 

 only to single families or genera. If these facts are compared with what occurs in 

 Gymnosperms, the ovules of Cycadeae must be classed with the marginal carpellary, 

 those of many Cupressineae with the superficial description ; while those of Taxus 

 are axial and terminal, and those of Salisburia lateral. 



When the position of the ovules is given, so also is some information as to their 

 morphological significance : the terminal ovules may be regarded as the terminal 

 portion of the axis, the lateral as equivalents of whole leaves, the marginal as branches 

 of leaves (lacinise, pinnae, or lobes) ; the superficial ovules may be included in the 

 category of such foliar outgrowths as we have already found to occur in the form of 



ovule is a metamorphosed segment of a carpellary leaf, a definition which Eichler has now accepted 

 (Bliithendiagramme, 11). A third view, the one stated in the text, is now held by many, that, as in 

 the case of the placenta, the morphological value or 'dignity' of the ovule is not always the same. 



Of these views, the one which aj)pears to be the most true to nature is the one which allows 

 the greatest latitude : but it is not always possible to refer an ovule to one of the categories, 

 caulome and phyllome, for its position does not necesmrily indicate its morphological significance. 

 Thus, a lateral ovule, as in Composite and Primulacese, might be either a leaf or a bud ; its probable 

 leaf-nature in these cases depends entirely on teratological evidence, which is of very doubtful value, 

 for an organ in a monstrous condition does not necessarily assume its primitive archetypical form. 

 Again, an organ borne by a leaf does not necessarily represent some typical part of the leaf, witness 

 the adventitious buds which are developed on leaves in many cases, and the ovules which cover the 

 surface of the carpels in Nuphar luteum and Brasenia peltata (Strasburger, Angiospeimen und Gymno- 

 spermen, p. 57). 



The difficulties met with in endeavouring to regard the ovule as a caulome or a phyllome may 

 be got over by regarding it as an 'emergence' (Strasburger, loc. cit.), borne sometimes on an axial, 

 sometimes on a foliar member. This view, to be completely satisfactory, ought to be applicable 

 also to pollen-sacs and to the sporangia of the Vascular Cryptogams. This cannot be quite accu- 

 rately done, for an emergence (p. 162 ante) is described as being developed not only from the 

 epidermal layer but also from the subjacent cells of the organ bearing it ; and we know that the 

 sporangia of the Vascular Cryptogams (except those of Isoetes) and the pollen-sacs of Pinus are 

 derived from one or more epidermal cells. Goebel (Bot. Zeitg. 1881) has expressed the opinion that 

 a sporangium (ovule, pollen-sac) is simply a sporangium, an organ srn generis as much as a stem or 

 a leaf. 



A few words may be added here with reference to the morphological significance of the integu- 

 ments of the ovule. The view has been often expressed that the integuments of the ovule are 

 homologous with the indusium of Ferns; this is opposed by Strasburger (Angiospermen und 

 Gymnospermen) and by Goebel (Bot. Zeitg. 1881) on the ground that the integuments arise from 

 the ovule itself, whereas the indusium is an outgrowth of the leaf bearing the sporangium. These 

 organs are analogous, but not homologous.] 



