36 CALIFORNIA ACADEMY OP SCIENCES. 



the production of some of the forms. But even in cases 

 where the change lasts only as long as the altered envi- 

 ronment is operative, although the permanent transmis- 

 sion of acquired characters is not demonstrated, it is 

 rendered highly probable. Cunningham gives an excel- 

 lent analogy illustrative of this. He says:* " If a plant 

 with a vertical stem is placed in a horizontal position, 

 the light coming from above, the end of the stem will 

 bend up toward the light, partly by growth, partly by 

 flexure. Such a plant was so placed, and, after a certain 

 time, when the upward flexure was established, it was 

 turned round so that the tip pointed downwards. Of 

 course the flexure was gradually reversed until the tip 

 pointed upwards again. After the same interval the 

 plant was reversed once more. This was continued for 

 some days, the plant being reversed at regular intervals. 

 At last, when the time came for turning the plant round,, 

 the operation was not performed, it was left undisturbed. 

 But then the plant began to reverse its flexure of its own 

 accord, and actually turned its tip downwards, away 

 from the light. By the regularly repeated reversal of 

 position a rhythm had been set up in the life of the 

 plant, and even when the cause which excited this 

 rhythm ceased, the rhythm continued." 



Weismann himself gives some instances of these 

 " after-effects " in plants, such as the case of the sun- 

 flower, which is as follows:! " If vigorous plants of the 

 sunflower, grown in the open air, be cut off close to the 

 ground and transferred to complete darkness, the exam- 

 ination of a tube fixed to the cut surface of the stem 

 will show that the escape of sap does not take place uni- 

 formly, but undergoes periodical fluctuation, being 



strongest in the afternoon and f weakest in the early 







* The New Darwinism, Westminster Review, July, 1881, p. 416. 

 t Essays upon Heredity, 1891, I. p. 416. 



