5l8 PHANEROGAMS. 



the inner the body of the root. The dermatogen, pushed outwards by the 

 development of the body of the root, produces the root-cap in the way already 

 mentioned ; the tissue of the body of the root itself which is covered by it becomes 

 differentiated into plerome and periblem. The same process takes place in Pistia, 

 and probably also in Grasses. Hanstein and Reinke do not find 'anywhere an 

 apical cell which originates the growth, as in Cryptogams ; a group of cells always 

 obeys the common direction of growth.' 



The variation in the size of the embryo in the ripe seed of Angiosperms has 

 already been mentioned w^hen speaking of the endosperm. The external differ- 

 entiation sometimes goes no further than the rudiment of the root (radicle) at the 

 posterior end of the stem of the embryo and the cotyledons {e.g. in Cucurbita, 

 Helianthus, Allium Cepa, &c.), between which lies the naked punctum vegeiaiionis. 

 But frequently this latter undergoes further growth before the seed is ripe, and 

 produces additional foliar structures (as in Grasses, Phaseolus, Faba, Quercus, Amyg- 

 dalus, &c.), which are then included, in the ordinary nomenclature, under the term 

 Plumule, but do not unfold until the germination of the seed. The systems of 

 tissue are usually sufficiently clearly differentiated as such at the period of maturity 

 of the seed ; but the different forms of permanent tissue do not become developed 

 till later, during germination. A striking exception to this advanced development 

 of the young plant within the ripening seed is afforded by parasites and saprophytes 

 destitute of chlorophyll, but especially by Orchidese. In them the embryo remains 

 until the seed is ripe as a roundish corpuscle consisting sometimes of only a few 

 cells, without any external differentiation into stem, leaves, and root; this takes 

 place only after germination, and even then sometimes quite imperfectly. 



Development of the Seed and Fruit. While the endosperm and embryo are 

 becoming perfectly formed in the embryo-sac, growth proceeds not only in the 

 ovule but also in the wall of the ovary that encloses it. Since the testa is formed 

 at the expense of the whole or part of the cellular layers of the ovular integuments, 

 and presents extreme diversities in its structure, the ovule, together with its contents 

 which have resulted from fertilisation, becomes the Seed. The wall of the ovary, 

 the placentae, and the dissepiments, not only increase in dimensions, but undergo 

 the most various changes of external form and still more of internal structuie. 

 Together with the seeds they constitute the Fruit. The transformed wall of the 

 ovary now takes the name of Pericarp ; if an outer epidermal layer is specially 

 differentiated it is called the Epicarp, and an inner one the Endocarp ; while a 

 third layer, the Mesocarp, frequendy lies between these two. A number of typical 

 kinds of fruit are distinguished according 'to the original form of the ovary and the 

 structure of its tissue when ripe, the nomenclature of which will be given in the 

 sequel. But sometimes the long series of deep-seated changes induced by fertili- 

 sation extends also to parts which do not belong to the ovary, and even to some 

 which have never belonged to the flower. But as they are part of the fruit from 

 a physiological point of view, and are usually associated with it as a whole, while 

 sharply differentiated from the rest of the plant, a structure of this kind (such as 

 the fig, strawberry, and mulberry) may be termed a Pseudocarp. 



At a certain period either the fruit together with its seeds becomes detached 

 from the rest of the plant, or the seeds alone separate from the dehiscent fruit ; and 



