DIV. I 



MORPHOLOGY 211 



are hygrophilous. This power of reacting to different environments 

 by the development of different characters is known as the capacity 

 of modification. Such MODIFICATIONS (cf. Physiology, p. 322) are 

 not inheritable in the sense that the seeds of, for example, an am- 

 phibious plant which has developed in water to a water plant will 

 produce the aquatic form if they are sown on land. On the contrary, 

 the land form is always produced on land and the aquatic form in water 

 whether the seeds have been taken from the one form or the other. 



These influences of the environment have been regarded as direct 

 adaptations on the part of the plant which has the power of thus 

 modifying itself. The power has further been attributed to the 

 organism of responding by a useful reaction to every external influence, 

 even to those not met with under natural conditions. Such a power 

 of adaptation would apply to new functions as well as to external 

 factors ; the need of an organ would bring about its formation. It is 

 further assumed by Lamarckism that every modification, especially 

 those resulting from external factors or the needs of the organism, is 

 inheritable, or at least can become inheritable in the course of time. 

 Thus when a plant has been for generations directly adapted to aquatic 

 life, to life in the shade, or at the expense of another organism, the 

 acquired peculiarities of structure gradually become fixed, i.e. they 

 also appear when the occasion for them is no longer present. 

 Regarding this view it must first be remarked that the assumption 

 "a need for an organ can bring about its formation" is not clear, and 

 also that nothing is known of the inheritability of those effects of 

 external conditions that have been termed modifications above. For 

 these reasons alone Lamarckism must be given up. Further, it is 

 difficult to conceive that the organism should react usefully in 

 anticipation of particular external factors. As a matter of fact we 

 not uncommonly meet with reactions to new unaccustomed stimuli 

 which appear quite indifferent or even harmful. Thus the tentacles 

 of Drosera become curved at a high temperature just as if they were 

 in contact with an insect. Leaves cut off from a plant may continue 

 to live for years by producing roots even when they are unable to 

 form shoots. When there appears to be direct adaptation to various 

 stimuli (e.g. water, light, air, shade, etc.), to which particular 

 organisms are exposed in their habitats, the result may be otherwise 

 explained. It may be assumed that such organisms already possess 

 the capacity or the factors which enable them to follow this or that 

 course of development according to the external conditions. The 

 external conditions would not produce the factors but only determine 

 their becoming manifest or not. How these factors have historically 

 come about, and why some organisms possess them and others not, 

 why, for example, only some plants are adapted to live in water as 

 aquatic plants or as land plants on the land, remains still unexplained. 

 On this question Lamarckism throws no light. 



