Plants, and Parthenogenesis. 83 



Robert Brown, between 1831 and 1833, repeated and con- 

 firmed, to the fullest extent, the discovery of Amici in the case 

 of the families of Orchidacere and Asclepiadace?e. Amici, be- 

 sides, very correctly showed that the elongation of the inner 

 coat of the pollen-grains (usually regarded as simply an act of 

 extension) was effected by a process of growth at the expense of 

 the fluid supplied by the surrounding conducting cellular tissue. 

 The end of the pollen-tube in contact with the ovule Schleiden 

 followed and traced into its tissue, and came to the conviction 

 that, in a large number of plants, the primary formation of the 

 embryo takes place in the interior of this intruded sac of the 

 pollen. 



Horkel, Wydler, and, in part, Meyen, accepted Schleiden's 

 views ; and Schacht, in his extended prize essay sent to the 

 Royal Netherlands Institute, contributed a large number of 

 proofs in support of Schleiden's discovery. Repeated experi- 

 ments and investigations that I undertook also caused me to 

 side in general with this observer, although I held the opinion 

 of Meyen and Brongniart to be generally true, that only the 

 union of the contents of the two heterogeneous cells — viz. of the 

 pollen- cell and of the embryonic sac — is necessary, according to 

 the osmotic capacity of the membranes concerned (at one time 

 of the pollen tube, at another of the embryonic sac) or through 

 the union of these two histological elements, to give rise to the 

 development of a new individual. 



In the mean time, Griffith (in 1835, at Calcutta) saw, in 

 Santalum album and in Osyris, the outgrowth of the embryonic 

 sac, in the form of a tube of greater or less length, from the 

 naked ovules as far outwards as the funiculus. The develop- 

 ment of the plant-germ only proceeded when the pollen-tube 

 entered within this open and freely-exposed cavity of the em- 

 bryonic sac. On the other hand, in Viscum the germ appeared 

 to him to take its origin in the pollen-tube itself. 



In 1846, Amici, Mohl, and Hoffmeister pronounced them- 

 selves decidedly in favour of the opinion that the germ never 

 originates within the pollen-tube, but by the enlargement of one 

 of the cells floating freely in the fluid of the embryo-sac, after 

 the pollen -tube has so extended itself as to reach to the vicinity 

 of that sac. 



Subsequently to these different interpretations as put forward 

 by various able observers, Schleiden suggested the probability 

 that the opinion first advanced by Brongniart might in many 

 cases be true, and that the germ took its rise from the conjuga- 

 tion of the pollen-tube with a pre-existing embryo-vesicle. At 

 the same time the last-named naturalist, and, at a later period, 

 Radlkofer, and, last of all, Schacht, from his observations in 



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