128 ANATOMY AND PHYSIOLOGY OF 



tion, and, by lais researches on tlie impregnation of the Orchidese (" Sulla 

 fecundazlone delle Orchidee^' — Giorn. Bot. Italian. Anno 2), made an end of 

 the new theory at one blow. Amici's treatise was soon followed by a 

 confirmation of what he had seen by mybelf (" JBot Zeifung'' 1847, 465), 

 and others ; and these were quickly succeeded by the extensive researches 

 of Hofmeister (" Die Entstehung d Embryo d. EhaneTogammC^ and of 

 Tulasne (" Ann. d. Sc. nat 3 Ser. xii), which contained a full confirmation 

 of the results obtained in the Orchidese, and demonstrated that the im- 

 pregnative process is the same in its essential circumstances throughout 

 a long series of Phanerogamia, so that this subject may be considered as 

 quite settled in its principal features. 



Ohs. 2. The so-called naked-seeded Dicotyledons (the Cycadese and 

 Coniferse) present some very important differences from all other Phane- 

 gamia, in reference to the production of their embryo ; the circumstances 

 are unfortunately not all cleared up by the foregoing researches. The 

 differences depend, not so much upon the fact, that the pollen-grains fall 

 immediately upon the naked ovules in these plants, for nothing is essen- 

 tially altered by this, since the pollen-grains here germinate on the point 

 of the nucleus in the same way as in other plants, and are thus spared the 

 circuitous route which the pollen-tubes have to make through the con- 

 ducting tissue of the pistil. The distinctions lie in a great compHcation 

 of the structure of the ovule, ajid in the manifold deviations in the struc- 

 ture of the embryo. 



In the Coniferse, the nucleus is in great part displaced by the enlarge- 

 ment of the embryo-sac ; the latter becomes filled with cellular tissue, 

 out of which from three to six cells, arranged in a circle near the upper 

 end, become more considerably enlarged than the rest, and these consti- 

 tute what are caUed, by Robert Brown, the carpuscula^ — ^by Mirbel and 

 Spach, the secondary emhryo-sacs, — and also become filled up with cellular 

 tissue. The pollen-graixis germinate on the point of the nucleus, and send 

 down their tubes through the upper part of it j and the slowness with 

 which this process takes place in many species is remarkable, for in Larix 

 europcea^ according to G61eznoff, the pollen-tubes do not emerge from the 

 granules till after thirty-five days ; and in Pinus syhestris, Pineau states 

 that fall a year passes before they grow down through the nucleus to the 

 embryo-sac, whereby evidently the impregnation is also postponed for this 

 long period. When the poUen-tubes have arrived at the embryo-sac, they 

 break through it, and through the cellular tissue lying between its mem- 

 branes and the secondary embryo-sacs. The observations on their subse- 

 quent course are discordant. Pineau believed he had discovered that the 

 ends burst, and poured out the fovilla into the secondary embryo-sacs. 

 According to G616znoff, the pollen-tubes would break through an inner 

 membrane immediately enclosing the fovilla, and grow into the secondary 

 embryo-sac. In like manner, there is an obscurity as to the origin of the 

 embryo. Apparently there originates in the secondary embryo-sacs, 

 from the cells already contained in them, a pro-embryo of most peculiar 

 form : ia Finus, the upper part of it is composed of a rosette of four to 

 five cells, to which an equal number are applied below, these extend them- 

 selves into a long filament, which again bears four cells at its extremity 

 constituting the rudiment of the embryo. As the intermediate cells 

 grow down in the filamentous form, they break through the lower end of 



