11:^ 



I'LANT STUDIES 



Fig. 110. A ]ioIk-n grain (spore) from the 

 ]iiiu', wiiicli ilr\-el()])s wings (;rl to assist 

 ill its lianspnrtatiiju by curreuts of air. 



It is evident that for 

 tlie germination of seeds 

 liglit is not an essential 

 condition, for tliey niay 

 germinate in tlie liglit or 

 ill tlie dtirk ; Init the need 

 of heat, moisture, and 

 oxygen is very a.])])u.rent. 

 The amount i>f heat re- 

 quired for germination 

 varies widely witli iliiferent 

 seeds, some germinating 

 at mucli lower temjiera- 

 tures than others. Every 



kind (if seed, or spore, or egg has a special temperature 



range, lielow which and ahovc which 



it cannot germinate. The two limits 



of tlie rtinge may be called the 



lowest and highest points, but be- 

 tween the two tliere is a best point 



of temperature for germination. The 



same genertil fact is true in reference 



to the moisture supply. 



74. Dispersal of reproductive bodies. 



— Among tlie most striking external 



relations, however, tire those con- 

 nected widi the disperstil of sjiores, 



gajiietes, tind seeds. Spores and 



see(ls must lie ctirried tiwtiy from the 



ptu'cnt iihtiit, ttnil separated from 



eacli other, out of the reach of 



rivali'y for nutritive materitil ; ;ind 



gametes must come together and „ ., 



'^ '^ , FLii. 111. .\ piiil ol lireweeii 



lili^nd to form the eggs. Conspicuous (/■./);/(i/,i««,i ,,|„niiig and 

 among tlie means of transfer are the exposing iispinnu.i.see.is 



' . \\'liicli arc lraiis|M)rlc(l by 



following. the wiu.l.-AfUT Beal. 



