584 PHA NEROGA MS, 



Cactus, and Malvd) ; while sometimes the cavity of the tube becomes wider (as in 

 Oenothera and Cucurbitacese). Its contents consist of granular protoplasm, usually 

 mixed with a number of starch-grains (the Fovilla). 



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

 the naked apex of the embryo-sac, or, as in Watsonia and Sanialum, with the pro- 

 jecting striated ends of the synergidae; but very commonly a portion of the tissue of 

 the apex of the nucellus still remains through which it has to make its way to the 

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

 inflexed by the advancing end of the pollen-tube, or even perforated. 



[Strasburger has carefully studied^ the process of fertilisation in Torenia astatica, 

 Gloxinia hybrida, various Orchids, Monotropa, and Pyrola. He finds that when the 

 pollen-tube first (jomes into contact with the synergidae or with the embryo-sac, one 

 or both of the nuclei can be distinguished in it near its apex. These very soon 

 disappear, and its contents present a highly refractive, finely granular appearance. 

 The appearance of one or both of the synergidae now begins to change ; its nucleus 

 and its vacuole disappear, and its protoplasm becomes uniformly and highly granular, 

 closely resembling in appearance the contents of the pollen-tube as described 

 above; it loses its form, becoming irregular, and it is closely attached to the oosphere; 

 portions of it may break off and fasten on to the oosphere here and there. The 

 oosphere now becomes granular, and two nuclei can be detected in it; one of these is 

 the nucleus of the oosphere (the female pronucleus), the substance of the other (male 

 pronucleus) has doubtless been derived, through the synergidae, from the pollen-tube. 

 These two nuclei meet and coalesce, constituting the nucleus of the oospore; this 

 nucleus is often seen to contain two nucleoli, the nucleoli of the male and female 

 pronuclei, which coalesce somewhat later : the oosphere now surrounds itself with a 

 cellulose wall, and with this its conversion into the oospore is complete.] 



The further 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 oospore. 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, JEsculus, 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 May 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 Liliaceae it is common for the ovary to commence growing 

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

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

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

 fertilisation ; 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.) 



^ [Befruchtung und Zelltheilung, 1878, p. 52.] 



