PHYSIOLOGY OF REPRODUCTION IN PLANTS. 247 



offered on the polymorphism of the lower green Algae, stands 

 so firmly on the new foundations which Klebs gives it, that 

 one is constrained to believe much of this work must be re- 

 examined by the help of the strict methods enjoined by 

 him. 



Thirdly, the especial object of the work is to show that, 

 having learnt to isolate and grow a green Alga, its behaviour 

 will vary according to the conditions of the environment. 

 This of course would be generally conceded, but the point 

 is that the exact conditions which induce or govern a given 

 biological reaction can be discovered and controlled, and so 

 our knowledge is altered from an indefinite conviction that 

 you must not do this, that, or the other, to an Alga, or it 

 will not grow, or multiply, or succeed generally, to the 

 definite surety that it you want a given Alga to produce 

 zoospores you must treat it in such and such a manner, and 

 if you alter the treatment according to directions you can 

 make the Alga form sexual organs, and so on. 



It sounds almost absurdly impossible when put in such 

 a form, and yet many of Klebs' experiments show that his 

 fifteen years or so of study of these reactions have resulted 

 in knowledge so clear and so definite of the exact conditions 

 necessary to induce a given biological response, that one 

 may almost compare the operations with those of a chemist 

 who calls forth a predicted change in a substance in a test 

 tube by adding another substance to it. 



When we are told that Conferva, for instance, after 

 being cultivated for twenty-two days in a i per cent, 

 galactose solution, in which it forms no zoospores, at once 

 proceeds to form them if transferred to a solution of 

 aesculin, and that the whole experiment is carried on in 

 the dark, our ideas begin to receive shocks which lead us 

 on from total revolt to wondering acquiescence and convic- 

 tion in proportion to our acquaintance with the number 

 of recorded experiments, the care and fulness of the re- 

 cords, and the character of the evidence generally. 



But the work teems with equally startling results, of 

 which I shall have space to quote a few instances only. 



VancJieria rcpens, if growing on solid media in damp 



