- 1 ^ PHA NER OGA MS. 



ing quickly in length ; after entering the micropylc its wall generally thickens 

 rapidly and often considerably, chiefly, as would seem, by swelling, so that its cavity 

 forms only a narrow channel. Hofmeister compares it, in this condition, to a ther- 

 mometer-tube (as e.g. in Lilium, Cactus, and Malva) ; while sometimes the cavity of 

 the tube becomes wider (as in CEnothera and Cucurbitaceoe). It consists of granular 

 protoplasm, usually mixed with a number of starch-grains (the Fo villa). 



Within the micropyle the pollen-tube either comes immediately into contact 

 with the naked apex of the embryo*sac, or, as in Watsonia and Santalum, with the 

 projecting filiform apparatus of the embryonic vesicles; but very commonly a portion 

 of the tissue of the apex of the nucleus still remains through vrhich it has to make its 

 way to the embryo-sac. The wall is often weak at the apex of the embryo-sac, and 

 is frequently inflexed by the advancing end of the pollen-tube, and in Canna is even 

 perforated. 



The contact of the pollen-tube with the apex of the embryo-sac or with the 

 filiform apparatus of the embryonic vesicles is sufficient for the transmission of the 

 fertilising substance ; and the results of this process can usually be observed after a 

 short time in the behaviour of the nucleus of the embryo-sac and of that of the 

 embryonic vesicle. It frequently however occurs that a considerable time elapses 

 after the entrance of the pollen-tube before the commencement of the development 

 which is induced by it ; several days or even weeks in many woody plants, as 

 Ulmus, Quercus, Fagus, Juglans, Citrus, /Esculus, Acer, Cornus, Robinia, &c. ; 

 almost a year in the American oaks, the seeds of which take two years to ripen ; 

 in Colchicum autumnale the pollen-tube enters the embryo-sac at the latest at the 

 beginning of November, but it is not till ^lay in the next year that the formation 

 of the embryo begins. (Hofmeister.) 



Even the advance of the pollen- tube through the conducting tissue of the style 

 and into the cavity of the ovary often causes extensive changes in the flower; if the 

 perianth is delicate it usually loses at this time its freshness, fades, and afterwards 

 entirely falls off; among Liliacece it is common for the ovary to commence growing 

 actively even before the fertilisation of the ovules (Hofmeister) ; in Orchidea) not 

 only is the active growth of the ovary, which often lasts for a considerable time, 

 occasioned by polhnation, but the ovules themselves are by it rendered capable of 

 receiving impregnation ; in some cases even their production is thus induced from 

 the placenta which would otherwise remain sterile. (Hildebrand : see also Book III 

 on the Sexual Process.) 



Results of Fertilisation in the Embryo-sac ; Formation of the Endosperm and 

 Emhryo. The first result of fertilisation seen in the embryo-sac is (as Hofmeister 

 has shown) the disappearance of its nucleus; the action of the pollen-tube on the 

 embryonic vesicle is only apparent later ; the vesicle becomes enclosed in a cell-wall 

 of cellulose if it did not possess one before fertilisation, as occurs sometimes, accord- 

 ing to the same authority {e.g. in Nuphar, Tropseolum, Cheiranthus, Funkia, Crocus, 

 &c.). The formation of the endosperm very commonly begins even before the 

 division of the embryonic vesicle, at the latest during its transformation into the 

 pro-embryo. In all Monocotyledons and most Dicotyledons the endosperm-cells 

 are formed simultaneously in large numbers by free cell-formation within the 

 parietal layer of protoplasm of the embryo-sac. They are at first globular and 



