54 TRANSACTIONS, NATURAL HISTORY SOCIETY OF GLASGOW. 



even with the embryo-sac. In like manner, the 

 small size of the microspores in comparison to the 

 large macrospores of Selaginella and other hetero- 

 sporous cryptogams is explained by the greater 

 necessity for dispersing the male element. The 

 minuteness of the antherozoids of Ferns, Horsetails, 

 Mosses, etc., is also determined in relation to their 

 dispersion. 



(2) The distribution of a plant also depends on 

 the number of seeds or spores to which it gives 

 rise. Bodies intended for wide distribution must 

 be produced in large numbers. Here, again, the 

 adaptation in seeds, and especially in spores, is very 

 obvious. A single plant of Sinapis nigra has been 

 known to yield 8,000 seeds, a single poppy 60,000 ; 

 Darwin computed that an orchid might yield 

 12,000,000 ; while the number of spores produced by 

 any ordinary Fern or Fungus defies computation. 



We may also note here the much greater 

 abundance of male than of female cells. The 

 antherozoids of any j^lant far exceed in number the 

 oospheres to which it gives rise. The pollen-grains, 

 again, far outnumber the ovules ; and in wind- 

 fertilised plants like the Pine, which throws out 

 clouds of pollen, the numbers are out of all 

 proportion. 



Seeds, as a rule, are larger bodies than spores, 

 and produced in much less profusion. This inferiority 

 in relation to dispersion explains why Phanerogams 

 are generally much more limited in their geographical 

 range than Cryptogams. The larger size of seeds 

 also renders necessary special adaptations in form 

 and structure "«'hich are not met "vvith in the spores 

 of flowerless plants. 



Dispersion may be effected by any of the following 

 means : 



1. The locomotion of the plant itself ; 



2. The vital activity of the germ ; 



3. Hygroscopic action and Turgescence ; 



4. The agency of Water-currents and Ice ; 



