Prof. H. Karsten on the Vegetable Cell. 479 
anfr. nucl. ili., levibus, tumidis, apice submamillato, subdeclivi; 
norm. vi., tumidis, suturis impressis ; costis radiantibus cire. xiv., 
haud 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., haud decussatis ; apertura subquadrata ; columella 
haud truncata, obtuse angulata ; labro acuto, a costulis indentato ; 
labio inconspicuo. Long. *21, long. spir. +16, lat. 06 poll., div. 20°. 
[To be continued. | 
XLV.—Histological Researches on the Formation, Development, 
and Structure of the Vegetable Cell. By Prof. H. Karsren, 
[Continued from p. 435.] 
& VEL 
The Development of Pollen.—Historical notes.—Origin of pollen, in 
Althea 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 ; Génération 
et Développement de l’Embryon, 1827) was the first to observe 
that, in the congeries of cells in the anthers of Cobea, 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 growth 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 des Pol- 
lens, 1842) 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 
