394 Plants wJiidi dissipate Energy. [Sess. 



be struck with the great similarity of form that exists, par- 

 ticularly in reproduction, between the green alga? and the 

 moulds. Compare a Vaucheria with a Pythium, a Spirogyra 

 with a Mucor [slides of these were shown under the micro- 

 scope]. It may be asked, How has that extreme likeness of 

 form arisen, associated with an enormously great difference 

 in habit ? We can imagine how in all probability the trans- 

 formation took place. Look at a Spirogyra filament going to 

 fruit : some cells of the filament may be found dead and 

 quite empty, and others living and apparently healthy. The 

 contents of the empty cells have evidently gone to nourish 

 the living cells, and so the saprophytic habit has been initi- 

 ated. We may support the guess by experiment. Put some 

 filaments of green alga in a weak solution of sugar in darkness, 

 and they will grow for some time : the alga lives temporarily 

 like a saprophyte. 



Last year we saw good reason to conclude from our study 

 of alga? that sex had its origin in a union of two or more 

 little cells to increase the mass of the new individual — to 

 increase its vital capital ; and we saw that sex was developed 

 and specialised more and more by adversity. In the great 

 uniform ocean the green seaweeds are mostly asexual. It is 

 when they take possession of rivers and lakes, and are sub- 

 jected to sudden changes of drought and frost, that they 

 develop the complicated phenomena of sex. This winter we 

 cannot fail to have been struck with the converse. As we 

 study fungi, from the lowest to the highest forms, we see sex 

 becoming less and less pronounced, as the saprophytic organism 

 becomes more developed. I have spoken much of sex. Why 

 so ? Because it forms the basis of all classifications of plants ; 

 and a classification to be good should show genetic relationships. 

 Even the artificial classification of Linnaeus is founded on the 

 rough and ready way of counting the stamens and pistils and 

 noting their arrangement, and this is sufficient in many cases 

 to indicate great natural orders. Why should this be so ? 

 Because the forms in which sex manifests itself record so 

 many different stages in the evolution of plant-life in the long- 

 past. 



Fungi have an extraordinary power of manufacturing en- 

 zymes, the so-called soluble ferments. One of these enzymes 



