ODCHID CONFERENCE. 



403 



At the upper end of the ovule Ues a minute but definite mass of 

 Hving substance or protoplasm, which we may describe as the repre- 

 sentative of the seed-parent or as the egg-cell. To this egg-cell a similar 

 living mass derived from the pollen tube makes its way, and so repre- 

 sentative cells, one of the seed parent and one of the pollen parent, lie 

 close beside one another. Each consists of a denser central body called 

 the nucleus and a more watery envelope of cytoplasm. The two repre- 

 sentative cells fuse with one another — nucleus with nucleus and 

 cytoplasm with cytoplasm — and so form a single cell with a single 



Fig. 141.^ — Diagrammatic Section of Flower of Helianthemum marifolitjm, 

 SHOWING Pollen Tubes. 



P.T. pollen tubes growing through S, the style, passing into OV^, the ovary, 

 and each reaching ]M, the micropyle of OV, an ovule. {After Kerner and 

 Oliver. ) 



nucleus. This cell, which, because of its two- fold origin, is called the 

 zygote, undergoes growth and division, and gives rise to the embryo 

 or plantlet of the seed. The adult plant is derived exclusively from 

 the zygote, which, in turn, is formed by the union of the two repre- 

 sentative cells. 



The essentials of this process of fusion are to be observed not in 

 flowering plants only, but also in all but the most rudimentary of the 

 lower plants. These essentials are to be discovered also in animals. 



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