158 The Field Naturalist 's Quarterly May 



formation of carbohydrates (starch, sugar, &c.) from raw 

 material under the direct influence of sunlight. This 

 process is now termed "photosynthesis," hitherto called 

 "assimilation of carbon." 



The mistletoe, that historic plant of mystic rites, is one 

 which plays a part in one of these partnerships. It is a par- 

 tial parasite — that is to say, that although it grows upon a 

 host-plant, from whom it derives a certain amount of sus- 

 tenance, it has green leaves of its own, and is therefore able 

 to make use of the C0 2 in the atmosphere. Mistletoe 

 grows upon various trees, such as apple, elm, or poplar, and 

 sends into the soft cortical layer of the branch upon which 

 it has established itself, its suckers or haustoria, and grows 

 fat upon the elaborated food which the host-plant intends 

 for its own use. Whilst the tree is enjoying its brief 

 summer, and working to provide against the days when, 

 shorn of its leaves, it takes an enforced rest, the parasite is 

 flourishing exceedingly and performing its own private 

 functions of flowering and producing fruit. But when the 

 tree is resting, the mistletoe, on account of its evergreen 

 leaves, is making good its shortened supply of food by 

 manufacturing some on its own account. Therefore scien- 

 tists advance the theory that the parasite is now a useful 

 companion to the tree, supplying a certain quantity of 

 elaborated food during this time to the host-plant. On 

 the other hand, may we not also surmise that the mistletoe, 

 having " short commons," does all it can to supply the de- 

 ficiency in its own larder, and that very little, if any, food 

 is returned to the tree ? So that it is a matter of opinion 

 whether this is a case of parasitism or of partial symbiosis ! 

 It is pretty certain that the mistletoe is not so distinctly 

 parasitic as to kill the trees upon which it grows. The 

 quality of the apples is possibly not improved, and this may 

 account for the increased cultivation of the mistletoe in 

 some districts, where it is considered of greater commercial 

 value than the apples themselves. 



It is said that a partnership exists between certain flower- 

 ing-plants and a fungus mycelium which invests their 

 roots, — the hairlike threads of the fungus, interwoven with 

 roots, underground of course, providing the phanerogam 



