THE AMERICAN 



MONTHLY 



MICROSCOPICAL JOURNAL. 



Voiv. XV. NOVEMBER, 1894. No. 11. 



The Geranium Leaf as a Cell Aggregate. 



By henry L. OSBOKN, 



st. paul, minn. 



with frontispieck. 



AH the higher or flowering plants, in common with all 

 living things whether plant or animal, are descended 

 directly or indirectly from a single ultimate cell — the 

 "egg-cell." The history of the plant as an individual is 

 the history of this cell, from the time of its fertilization 

 in the maternal ovule by the paternal pollen tube to the 

 time when the plant in its turn produces and matures 

 egg-cells and sends them out to play their part in the 

 cycle of life. The body of a mature plant is the sum of 

 the cells descended from the parental egg-cell in study- 

 ing which structure we are viewing the vast army of 

 progeny living or dead of the primary egg. In making 

 a histological study of any organism as complex as the 

 geranium leaf, it is very helpful to keep this fact con- 

 stantly before our minds and to raise the question in ex- 

 amining cells of each kind, what has been their origin 

 and to what other cells are these most closely related ? 



Cells in the immature portions of plants are soft walled 

 and delicate. If they should remain so, it is manifest 

 that the plant body could not attain any considerable 

 size because of the weight of the upper layers of cells on 

 those beneath, and that the plant could not live in the 

 air because they would be dried by evaporation and 

 thereby killed. The problem, therefore, for a plant liv- 

 ing like the geranium would be to obtain, in some way, 



