80 TKANSACTIONS AND PKOCEEDINGS OF THE [Sess. lxii. 



and prepare themselves for bestowing a similar service upon 

 the succeeding generation of leguminous plants. 



It must be evident that in all this complicated symbiotic 

 arrangement, an instance is presented to us of the danger 

 of proceeding to investigate a chain of natural phenomena 

 with a preconceived theory to which you hope that the 

 facts will accommodate themselves. According to Frank, 

 we are asked to believe that the plant baits its roots with 

 something nice, to lure the bacteria to it ; it opens the door 

 to them, and leads them along through a lane into the body 

 of the root, where they find a number of expectant cells 

 organising themselves for their reception. These surround 

 the bacteria as a kind of bodyguard, and conduct them to 

 the vessels that enable them to enter the circulation of the 

 plant. The plant constructs a special abode for them, and 

 supplies them with nourishment, whereby they may increase 

 and multiply ; and only when it requires a large amount of 

 albumen for the development and ripening of its seed; does 

 it claim back the albumen it had lent. At the same time, 

 with a prudent eye to the future, it allows a residue of the 

 organisms to escape into the soil, sufficient in number to 

 satisfy the requirements of all its progeny in the coming 

 season. The symbiosis consists in this, that the plant 

 supplies the bacterium with a breeding place and a store 

 of food, and receives from the bacterium in return a 

 stimulus which enables it to assimilate the free nitrogen 

 of the air. 



This is an interesting theory, but it will be thought by 

 many that it claims for the Leguminosa^ a little too much 

 intelligence, cunning, and providential care. 



There is a liability in working out a theory to select 

 (unconsciously it may be) only those facts which fit in with 

 it. Since the broaching of the symbiotic theory, other facts 

 have come to light that can scarcely be said to fit in with it. 



When llellriegel first recorded his experiments he claimed 

 for tlie nodules this advantage, that they enabled the young 

 plants to assimilate atmospheric nitrogen at the precarious 

 period of the youth when they had used up the nutriment 

 stored in the cotyledons, and were thrown upon their own 

 resources. This does not accord with the general experience 

 of investigators, who find that the advantage to tlie plant is 



