488 Organisms Are Products of Heredity and Environjnent unit ix 



Fig. 437 Sentinel Fine, Yosemite National Park. Its one-sided growth is caused by 

 wind. If seeds front this tree were planted in a sheltered valley how would the new 

 trees look? Would Lamarck have agreed with your answer? Explain, (u. s. depart- 

 ment OF interior) 



less well developed in the offspring. In 

 other words he believed that acqiiired 

 characters are inherited, even if only to 

 a very slight degree. Do you agree with 

 Larmarck? Do Exercises 6 and 7. 



Weismann's beliefs. Almost a century 

 after Lamarck, a German biologist Au- 

 gust Weismann (1834-1914) called at- 

 tention to this important fact: as the fer- 

 tilized tg^ (germ plasm) develops into 

 a new individual it produces both soma- 

 toplasm (tissue cells) and more germ 

 plasm (primary sex cells which later form 

 gametes). The diagram, Figure 438, 

 should make this clear. Since this goes on 

 in every generation, germ plasm is passed 

 on in an unbroken line. If the animal 

 should die without having reproduced, 

 that particular germ plasm dies off and 

 that line is broken. But under nonnal 

 conditions the animal does reproduce 

 and the germ plasm is immortal; it is 

 continued from generation to genera- 

 tion. Weismann spoke of this as "the con- 

 tinuity of germ plasm." Strictly speaking. 



then, offspring do not really come from 

 their parents; they come from the germ 

 plasm carried within the soma or body of 

 the parents. 



Since, according to Weismann, the 

 fertilized q^^ produces both somato- 

 plasm (tissue cells) and more germ plasm 

 (primary sex cells), it follows that the 

 primary sex cells are not made by the 

 body which houses them; they come 

 directly from the line of germ plasm car- 

 ried from earlier ancestors through the 

 parents. Examine the diagram again. 



Weismann believed that the sharp dis- 

 tinction bet\veen germ plasm and soma- 

 toplasm held for all organisms. But you 

 read earlier that while it does hold for 

 the more complex animals, it is not true 

 of some of the lower animals nor is it 

 true of plants. In these organisms, tissue 

 cells (somatoplasm) are capable of pro- 

 ducing reproductive cells. Therefore, we 

 now accept Weismann's statement as ap- 

 plying only to the more complex ani- 

 mals. 



