NUMBER OF SEEDS 



175 



the antherozoid ceased to swim and pollen-grains could be 

 conveyed through the air from flower to flower by wind or 

 by insect agency. 



The fact that the prothallus has been maintained in this 

 highly modified form in the higher seed- 

 bearing plants was for a long time not 

 recognized. But as the result of a series of 

 comparative studies there seems no doubt 

 that this is so. The seed which contains 

 the embryo plant is a direct development 

 of the ovule. It is detachable and con- 

 tains an embryo which will grow into a 

 new plant. It also contains food, gen- 

 erally in the form of starch and pro- 

 tein, for the embryo to live on. 



Number of Offspring 



The number of seeds is often very 



great. During one season the radish will 



produce 12,000 seeds, the plantain 



14,000, the shepherd's purse 64,000 and 



the tobacco plant 360,000. But perhaps 



the orchids show the greatest number ; 



a single plant of a certain genus known 



SisAcropera is said to produce 74,000,000 



seeds in one breeding season. 



Whenever you look at a garden or a , „ , 



J in i"j -4- • J u • 1 + Fig. 64. Ovary of Poly- 



wood or a field, it is seed-bearing plants ^^^^^ convolvulus during 



that you see. The others, non-seed-bear- fertilization; nu, nucellus; 



inff plants, are insignificant in compari- e, embryo-sac; ek, central 



•j.1 J.1 • J • J. 4. ^ nucleus of embryo-sac; ??, 



son With this dominant group; part of stigma;:?., pollen-grains; 7>5. 



their success is undoubtedly due to the pollen-tubes. Magnified 48. 

 fact that they protect the female repro- After Strasburger. 

 ductive cell within their own body, nourishing it and cherishing 

 it in every way. 



The plant as we see it is asexual; protected by numerous 

 coats and layers of cells is the embryo-sac, which "in a 

 manner of speaking," as John Silver used to say, is a parasitic 

 prothallus inside the asexual body of the sporophyte. 



