133 



IX. 



Plants in their relation to environment. How plants may be 

 naturally or artificially modified, in special organs, or in 

 their whole growth. Plant-breeding. 



G. KLEBS. Alterations of the Development and Forms of plants 

 as a result of Environment. (Abs. of the Croonian Lecture 

 delivered at the Royal Society on May 26th, 1910. Nature, 

 Vol. 83, June 2nd, 1910, p. 414). 



The fungus Saprolegnia is chosen as an example among the lower 

 plants. This fungus lives on dead insects, and shows three distinct 

 stages of development: i) vegetative growth of the mycelium; 

 2) asexual reproduction by motile zoospores ; 3) sexual reproduction 

 by male and female organs. Under ordinary conditions these three 

 stages follow one another quite regularly until, after ripening of the 

 resting spores, the fungus dies. But according to the special con- 

 ditions it is possible to produce a particular stage, and also to alter 

 the succession of the stages. 



Under very favourable conditions of nutrition the fungus must 

 continuously grow, without propagating and without dying. Nume- 

 rous other lower plants, as fungi and algae, show the same relations 

 to environment. 



Flowering plants present far greater difficulties in consequence 

 of their very complicated structure. 



Experiments were made, which are being continued, with Sem- 

 pervivum Funckii and Sempervivum acuminatum. Under veiy favou- 

 rable conditions of nutrition, a rosette ripe to flower can be trans- 

 formed again into a vegetative one, which must always grow without 

 sexual reproduction. We come to a new serie of forms by replacing 

 flowers by leaf-rosettes, which can be produced on all parts of the 

 inflorescence. The plants of which the inflorescence bears rosettes, 

 do not die at the end of summer, as is normal, but live another two 

 or more years, appearing in peculiar forms. 



