-;2 PHANEROGAMS. 



Li long tube, and emitting after impregnation one or more vermiform protrusions 

 which penetrate into and destroy the tissue of the nucleus and of the integu- 

 ments, or even protrude altogether out of the ovule (as in Pedicuiaris, Lathrgea, 

 -ind Thesium). On the other hand in those plants in which the endosperm 

 originates by cell-division we learn from Hofmeister that the following variations 

 occur : — ' The whole of the cavity of the embryo-sac behaves like the first cell 

 of the endosperm in Asarineae, Aristolochiace^, Balanophoraceas, Pyrolese, and 

 Monotropeae ; the first division of the sac is the result of a partition-wall which 

 divides it into two nearly equal halves, each of which encloses a cell-nucleus 

 and again divides at least once into daughter-cells. In other cases the first 

 cell of the endosperm includes the upper end of the embryo-sac ; the embryo-sac 

 which has just been fertiHsed appears to be divided by a transverse septum into 

 two halves, the upper one of which developes into the endosperm by a series of 

 bipartitions ; while no such bipartition of the lower one occurs in Viscum, Thesium, 

 Lathraea, Rhinanthus, Mazus, Melampyrum, or Globularia. The first cell of the 

 endosperm fills up the middle part of the embryo-sac in Veronica, Nemophila, 

 Pedicuiaris, Plantago, Campanula, Loasa, and Labiatse ; its lower end in Loranthus, 

 Acanthus, Catalpa, Hebenstreitia, Verbena, and Vaccinium.' In Nymphsea, Nuphar, 

 and Ceratophyllum, the upper end of the embryo-sac is cut off from the rest 

 of the space by a septum soon after impregnation, and the further development 

 of the daughter-cells or endosperm takes place only in the upper part which 

 also includes the ' embryonic vesicles.' This mode of formation of the endosperm 

 differs however from that which occurs in the plants mentioned above, in taking 

 place in the upper half of the embryo-sac by free cell-formation. 



In the very large majority of true parasites (except Cuscuta) and saprophytes, 

 the endosperm is formed by cell-division ; in Cuscuta however by free cell-formation. 

 Hofmeister states that only slight indications of the formation of endosperm are 

 to be found in Tropaeolum and Trapa. 



The mode of formation of the Emb}yn of Dicotyledons, as it has now been 

 elucidated by Hanstein's recent researches, has already been explained in the 

 introduction to Angiosperms (see Fig. 372, p. 516). It need now only be stated 

 in addition that in parasites destitute of chlorophyll and in some saprophytes 

 the seeds become ripe before the embryo has emerged from the condition of 

 a roundish mass of tissue still without external differentiation of parts {e. g. in 

 Monotropa, Pyrola, Orobanche, Balanophoraceae, and Rafiflesiaceae). 



With reference to the Formation of Tissue^, I will confine my remarks here to 

 a description of the behaviour of the fibro-vascular bundles and of the mode in which 

 the stem increases in thickness. 



With the exception of a few water-plants of simple structure, in which a purely 

 cauline fibro-vascular cylinder runs through the stem and increases in length at its 



^ Hanstein, Jahrb, fiir wiss. Bot. vol. I, p 23^ et seq., and for the girdle-shaped combinations 

 of vascular bundles Abh. der Berl. Akad. 1857, 8, — Nageli, Beitrage zur wiss. Bot, Leipzig, Heft I, 

 1858 ; and Dickenwachsthum und Anordnung der Gefassstrange bei den Sapindaceen, Miinchen 1864. — 

 Sanio, Bot., Zeit. -1864, p. 195 et seq. and 1865, p. 165 et seq. — Eichlcr, Denkschiift der kon. bayer. 

 bot. Gesells. vol. V, Heft I, p. 20, Rcgensburg 1864. 



