ISO AK ATOMY AND PHYSIOLOGY OF 



tlie whole, tKe funiculus coherent with the ovule forms a ridge running 

 along one side (the raphe), the hilum (the point of insertion of the funicu- 

 lus) lies beside the mieropyle, at the lower end of the ovule, and the axis 

 of the nucleus is straight. But when the nucleus itself is curved to one 

 side by an unequl growth of its two sides ; so that the micropyle comes 

 to lie beside the clialaza at the base of the ovule, and the highest point of 

 the ovule is formed by the curved side-wall, the ovule is called campylo- 

 tropous (kTwnmlaujig). 



Although not difficult of investigation, the knowledge of the structure 

 of the ovule advanced very slowly. An excellent foundation was laid by 

 Malpighi; but it was Robert Brown, who first opened the path to 

 further progress, by his desciiption of the ovule of Kingia, The researches 

 of Brongniart and Mirbel, which latter clearly unfolded the mode of ori- 

 gin of the different forms of the ovule from the orthotropous, but gave a 

 very incorrect account of the coats of the ovule, were followed by the ob- 

 servations of Fritzsche, who cleared up the latter point, and the extensive 

 investigations of Schleiden, who, through a large quantity of detailed re- 

 search, earned very great credit by making known the different modifica- 

 tions of the structure, — the varying number of the coats, — the universal 

 occurrence of the embryo-sac, — the origin of this from a cell, ko. Hof- 

 meister (" D. Entsteh. d. Mmhryo der Fhanerog. ") traced back the earliest 

 stages of development of the ovule further than any previous observer, and 

 found (in the Orchidese) that it takes its origin from a single cell of the 

 epidermis of the placenta this cell dividing by a cross section into two 

 cells, one lying above the other, the upper of which, is converted by further 

 subdivision into the cortical layer of the nucleus, and the lower, into the 

 central cellular cord, the uppermost cell of which becomes the embryo-sac. 



According to the ordruaiy view, the ovule is to be considered as a bud, 

 the axis of which is metamorphosed into the funiculus and nucleus, the 

 leaves into the coats of the ovule. The order in which the coats are de- 

 veloped, might certainly be fairly urged against this opinion ; but I can- 

 not question its correctness, since it is not unfrequent in malformed ovaries, 

 for the ovules to grow out into leafy shoots. 



"With regard to the physiological import of impregnation, it is perfectly a 

 matter of indifference whether the ovule is regarded as a product of the 

 carpellary leaves, according to the theory advocated by Bobert Brown 

 and Be CandoUe, or it is assumed, with Schleiden, Endlicher, and Unger, 

 and others, that the placenta is always an axial structure. It would lead 

 me too far to relate the reasons for and against these two theories ; each of 

 which is true of a portion of the Vegetable Kingdom, but neither of 

 which, and especially the latter, can be exclusively applied to all plants, 

 without coming into contradiction to the clearest facts. 



Detailed researches on the structure of the ovule are to be met with, 

 especially in the works of Mirbel ( " Bech. sur la struciure et devehppement 

 de Vovuh tiegUah,'"' Ann, desSc. nat. xvii), Schleiden (^" JJeK die, Bildung 

 de^ Eichens" Act. nat cur, xix. p. L ^^Grundz der wiss, Bota>ni7c'^)^ Hof- 

 mai^ter f'Die Bntstehung des Emlryo der Fhanerog^ and Tulasne (" Ann, 

 dm Sc, nat Zme S^er^ xii). 



"^^ The Origin of the JEmlryo. 



The impregnation of the ovule by the pollen is an indispensable 

 condition to the origin of an embryo in it. It is true that the 



