GRAFTS. 265 



are easily apprehended when we compare parasites 

 like the Mistletoe, Loranthus^ or even such root- 

 parasites as the Broom-rapes and theRhinanthoideae 

 with grafts ; but they also exist in the case of 

 many fungus-parasites, and we might almost as 

 accurately speak of graftijig some fungi on their 

 hosts as of infecting the latter with them, especially 

 when it is borne in mind that the effect of the 

 scion on the stock is by no means always to the 

 benefit of the latter, and that there are reasons for 

 regarding the action of some such unions as that 

 of a sort of slow poisoning of the stock by the 

 scion. Why do we not here say that the stock 

 has been infected by the scion ? 



The resemblances between pollination and the 

 infection by fungus hyphae may also be insisted 

 upon. If we take into account Darwin's remark- 

 able experiments showing that in " illegitimate 

 unions " the pollen exerts a sort of poisonous 

 action on the stigmas or ovules, it is possible to 

 arrange a series of cases starting with perfectly 

 legitimate pollinations where the pollen tube feeds 

 as it descends the style on materials provided by 

 the cells, and proceeding to cases where the 

 pollen is more and more merely just able to 

 penetrate the ovary and reach the ovules, to 

 the extreme cases where no union at all is 

 possible. 



Side by side with such series could be arranged 

 analogous cases where fungus spores can enter and 

 infect the cells of the host, and live symbiotically 

 with or even in them, or can penetrate only with 



