SEED- PLANTS. 305 



that is, the apex of the nucellus, and therefore also the micropyle which projects above 

 it, is turned towards the base of the funiculus, the ovule being bent sharply round at the 

 base of the nucellus, while the funiculus runs along the whole length of the ovule and 

 unites with the integuments or at least with the outer one ; where it is thus in union 

 with them it is termed the raphc; in this case the nucellus is straight. A much rarer 

 form of ovule is the curved or cainpylotropous, in which the nucellus itself together with 

 its integuments is bent round, and has its apex and therefore also the micropyle turned 

 towards its base ; here there is no union with the funiculus. These are however only 

 the most striking forms and they are connected together by intermediate ones. The 

 spot from which the ovules grow is named the placenta, and belongs to the floral axis, 

 or more usually to the sporophylls (carpels) themselves. The placentas in many cases 

 show no particular phenomena of growth, but they not unfrequently form projections 

 which assume the appearance of special organs and at length separate from the sur- 

 rounding parts. While after fertilisation the endosperm and the embryo are developing 

 in the embryo-sac, the former usually increases greatly in size, and takes the place of 

 the surrounding layers of tissue of the nucellus and sometimes even those of the inner 

 integument ; the tissue of the integuments which is not thus displaced, or more com- 

 monly particular layers of it, then becomes the seed-coat. If any portion of the tissue 

 of the nucellus, filled with food-material, remains till the seed is mature, it is distin- 

 guished as perisperm its nutrient contents, though lying outside the embryo-sac, are 

 consumed by the embryo as it unfolds, and the perisperm therefore may perform the 

 functions of the endosperm. The seeds of the Cannaceae and Piperaceae contain 

 perisperm. Sometimes, as the ovule developes into a seed, a new envelope grows up 

 round it from below, which covers the stout testa usually with a soft mantle, and is 

 termed an aril ; of this kind is the soft red envelope on the hard-shelled seed of Taxus 

 baccata, and the ' mace ' of the nutmeg which is the seed of Myristica fragrans. 



We found considerable variety in position and origin in the sporangia of the Vascular 

 Cryptogams ; in the majority of cases they grow from the surface or margin of the 

 sporophyll, or in its axil, or from a stem-structure ; there is a similar variety in the 

 point of origin of the ovule in the Phanerogams. In a few cases the orthotropous 

 ovule is the prolongation or termination of the flowering axis itself, so that the nucellus 

 actually is in the place of its vegetative cone, as in Taxus and the Polygonaceae ; 

 more commonly the ovule is a lateral shoot from beneath the apex of the floral axis, 

 as in the Primulaceae and Compositae ; but the most common case is where the 

 ovules spring from undoubted leaves, the carpels or sporophylls, and usually from 

 their margin, like pinnae from the leaf, of which a very striking example is to be seen in 

 Cycas ; it is less usual for the ovule to be formed on the upper (inner) side of the carpel, 

 as in Butomns, Akebm, Nyinphaea, and others. Sometimes the ovule is in the axil of 

 the carpellary leaf, as in the Cupressineae and Ranunculaceae. Relying on these cir- 

 cumstances of position of the ovule botanists have assigned to it different morphological 

 values, as stem-structure, leaf-structure, emergence, etc. ; or they have sought to show 

 by rather forced arguments that the ovule is everywhere a part of the leaf. The whole 

 discussion starts from the assumption that the sporangia or ovules must be referred to 

 vegetative organs or result from the metamorphosis of such organs ; but such an 

 assumption is quite incorrect; sporangia are distinct organs, as much as stems or leaves, 

 and we have a clear insight into the morphological nature of the ovule, and one 

 that requires no further explanation, when we know that it is simply a somewhat modi- 

 fied macrosporangium. The perception of this truth which was first obtained from 

 Hofmeister's investigations and has been confirmed by all later researches, but espe- 

 cially by those of Strasburger and Warming, is not assisted but hindered and obscured 

 by dwelling on the malformations to which ovules are very liable, while the relations 

 described above have been ascertained by the history of development. 



The carpels are the floral leaves which have the closest genetic and functional rela- 

 tionship with the ovules ; they either produce and bear the ovules or are intended to 



[2] 



