PLANT DEVELOPMENT. 



25 



to make tlie loaf last longer, is also composed of these fossils ; for whilst 

 the shell is flinty, the cell itself is rich in starch, which has been 

 preserved through countless ages. 



44. Dual Reproduction, Conjugation, — We here see 

 Dual Reproduction, or Paired reproduction (birth from two 

 individuals). At maturity the mother-cell divides into two 

 equal parts, called valves. Each valve is an individual 

 (Fig. 13, B), but it is incapable of reproduction by itself 

 alone. Presently two valves approach each other (Fig. 13, 

 C) ; their walls in the central part unite and then rupture, 

 so that their contents mingle in one mass ; this mass de- 

 velops a wall of cellulose (Fig. 13, D), and becomes a 

 spore called a Zygospore, or Jointspore (Gr. Zygob, I join). 

 Then the valves die, and the Zygospore becomes a complete 

 individual, rupturing into two valves like the parent. The 

 two valves thus produced are not apt to rejoin ; each seeks 

 a stranger ; thus showing that Nature, even in her lowest 

 types, teaches the advantage of cross-fertilization. This 

 mode is the first hint or prophecy of two sexes ; but 

 here, though the cells are separate, they are exactly 

 alike, and both are active. This mode is therefore 

 called Conjugation, or 

 Joining. 



45. Green Seaweeds. 

 — We next find a plant 

 which takes the form of 

 a branch, and fastens it- 

 self to the earth or stone 

 by projections which 

 serve the purpose of 

 hold-fasts, and sinmlate 

 roots ; but they are not 

 true roots, for they 

 have no power of ab- 

 sorption. This branch- 

 ing plant consists of a 

 single cell, like a glove 

 with many fingers. The ^"'- ''■^■—Bryopm piumosa, nat. size. 

 Vaucheria (Fig. 1) is an example; the lovely little Bry- 

 opsis (Fig. 15) is another. 



B 3 



