Organizaticyfi ifi Vhccnogamous Plants, 179 



jncontrovertibly (what is likewise established by the study of 

 development) that the pollen forms itself in the interior of the 

 leaf, and that therefore the anther cannot be considered as a 

 leaf rolled up either backwards or forwards, which produces 

 the pollen upon its surface. 



If we carry back our investigations of the anther as far as 

 its first appearance, we find that in every family it goes through 

 just the same conditions, and that all the apparently deviating 

 characteristics of this organ in the Orchidecc^ Asclepiadea;, Cu-- 

 curhitacece^ Stylidece^ &c., are merely later unfoldings of the 

 same fundamental type, and are only physiologically unim- 

 portant modifications of the same plan, which nature, here as 

 everywhere else where external differences of form only are 

 concerned, has made the subject of so great and wonderful 

 variety. 



The formation of the pollen takes place in this manner : 

 the four groups of cells intended for the pollen separate them- 

 selves from the remaining tissue of the leaf, their individual 

 cells continually increasing, and in the interior of each proba- 

 bly for the most part four other cells are formed, in each of 

 which a grain of pollen is produced, upon which the original 

 cells become entirely reabsorbed. The four pollen grains often 

 appear to be developed in one cell, if we decline the assuming 

 that the delicate cells, closely surrounding them, have been over- 

 looked. SometimeSj although seldom, there are only two grains 

 of pollen found in the larger original cell, for instance, in Po- 

 dostemo7i ceratophyllum^ which in that case afterwards remain 

 adherent one to the other, (figs. 29 and 30). Yet the quadru- 

 ple number is undoubtedly the general rule, which explains 

 the frequent occurrence o^polle?i quaternarium. 



If, however, the reabsorption of the original cells does not 

 take place, or is not perfect, a very peculiar arrest of develop- 

 ment occurs, which being the constant type in the OrcJiidecs 

 and Asclepiadece, has afforded botanists abundant occupa- 

 tion, whilst the entire peculiarity consists in this, that the pol- 

 len stops short at an earlier point in its development. This 

 same condition may be seen as a temporary stage in the de- 

 velopment of the flower of Picea and Abies in January and 

 February, in Finns in February and March, in which a loose 

 waxy pollen-mass may be found imbedded in each division of 

 the anther. At a somewhat later period we may see the four 

 cells in Picea and Abies, in which the four grains of pollen 

 lie closely united, and it ofiers a very pleasing spectacle when 

 we observe under the microscope each grain expand itself by 

 the absorption of water until it bursts its case in order to 



Y2 



