Prof. H. Karsten on the Vegetable Cell. 479 



anfr. nucl. iii., Isevibus, tumidis, apice submamillato, subdeclivi ; 

 norm, vi., tumidis, suturis impressis ; costis radiantibus circ. xiv., 

 baud contiguis, angustis, interstitiis undatis ; costulis rotundatis, 

 spiralibus, in spira iv., quarum postica multo minor, supercur- 

 rentibus, ad intersectiones subnodosis ; costulis circa basim sub- 

 rotundatam iv., baud decussatis ; apertura subquadrata ; columella 

 baud truncata, obtuse angulata ; labro acuto, a costulis indentato J 

 labio inconspicuo. Long. '21, long. spir. '16, lat. -Od poll,, div. 20"* 



[To be continued.] 



XLV. — Histological Researches on the Formation, Developmerd, 



and Structure of the Vegetable Cell. By Prof. H. Karsten. 



[Continued from p. 435.] 



§ VII. 



The Development of Pollen. — Historical notes. — Origin of pollen, in 

 Althaa rosea, from endogenous free cells with prolongations inwards of 

 the thickened walls of the mother cell. — Development of aculei on the 

 surface of pollen-grains. 



There is scarcely a vegetable tissue whose development has 

 been more frequently investigated than pollen. Adolphe 

 Brongniart (Annales des Sciences Naturelles, 1827 ; Generation 

 et Developpement de I'Embryon, 1827) was the first to observe 

 that, in the congeries of cells in the anthers of Cobcea, the pollen- 

 cells originated in fours. Mirbel made a more special study of 

 the development of the pollen of Cucurbita (Recherches sur la 

 Marchantia, 1833). He found that the granular contents of the 

 mother cell of the pollen became divided into four portions by 

 the inward grovvth of ridges from the sides of the cell towards 

 the centre, and that subsequently the outer surface of each seg^ 

 ment became hardened so as to form a smooth skin, within 

 which a second membrane was in process of time produced. 

 The very similar construction of spores and their development 

 occupied the attention of Mohl the same year (Entwickelung und 

 Bau der Sporen der kryptogam. Gew., Flora, 1833). The first 

 appearance of the spores of Riccia and Anthoceros was recog- 

 nized by Mohl under the form of four small collections of gran- 

 ules, each of which became enveloped by a delicate membrane. 

 These four masses contained in each cell assumed by mutual 

 pressure a three-sided, obtusely pyramidal form, whilst their 

 fourth side, lying in contact with the parent cell-wall, acquired 

 a convex outline. 



Subsequently, Nageli (Zur Entwickelungsgeschichte de& Pol- 

 lens, 1812) having extended and tested the application of 

 Schleiden's theory of cell-formation to the development of the 

 pollen-cell, and Unger (Ueber merismatische Zellenbildung bei 



