LECTURE XXIX. 



THE similarity between parents and offspring, though often very 

 great, is never exact. There are always greater or smaller differ- 

 ences observable. The similarity is usually very striking when the 

 two parents resemble one another very closely and come from the 

 same stock, and greatest of all when the contributing gametes are, 

 as in the case of some organisms (e.g. many of the Seed-Plants) 

 derived from the same individual. But even in these cases certain 

 differences are found. Some of these may be undoubtedly traced 

 to the action of the surrounding conditions on the developing 

 oosperm. Thus starvation may make the offspring of a vigorous 

 parent puny ; and its dwarfishness and its unhealthiness cannot be 

 said to be characteristics transmitted to it from its parent, but are 

 acquired from its conditions. Experimentally we may show diver- 

 gences brought about by differences in surroundings by taking a 

 number of seeds, formed when the pollen of a flower falls on its 

 own stigma, and sowing them under different conditions. The 

 seedlings which grow up in darkness are drawn and attenuated, 

 those which develop in absence of iron salts or of light are without 

 green colour, those which are surrounded with an excess of salinity 

 become more fleshy, those which lack various requirements are 

 weak and puny. Presumably each seed inherited very similar 

 qualities, but they acquire very different characteristics from the 

 action of their environment. That the majority of their character- 

 istics are inherited can scarcely be doubted, for no matter how 

 different the conditions of growth are, if life is at all possible, all 

 the plants are recognisable as being of the same kind as the parent. 

 This specific similarity cannot be attributed solely to the similarity 

 of conditions of nurture surrounding the early stages of the embryo, 

 for it is quite as marked in the lower plants where the oosperms 

 and spores begin their development outside the body of the parent. 

 Hence we recognise that the characters of each individual are 

 in' part inherited and in part acquired. It is interesting to note 

 that in spite of a very general popular belief to the contrary no 

 clear instance has been established of the transmission of such 



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