1889.] Tubercles on the Roots of Leguminous Plants. 



435 



into a hypha-like filament at the expense of the cell-contents. The • 

 further progress of this filament has already been described in my 

 memoir in the ' Philosophical Transactions ' for 1887. 



Before proceeding further, reference may be made to some re- 

 searches made during 1888 and 1889 with the object of learning more 

 about the conditions which rule the development of the tubercles, and 

 the relations of the organism to them. At first I set myself the task 

 of trying to discover a definite spore-stage, thinking that in the 

 rotting tubercles, or at the period of maturity of the plant, or at some 

 other time, it might be that the parasite would betray itself and 

 develop spores : this is not the case apparently, for my experiments 

 seem to prove conclusively that the well-being of the organism of the 

 tubercle and that of the pea or bean go hand in hand. This of course 

 is only so much evidence in favour of the view that we have here a 

 case of symbiosis of the closest kind, as expressed in my previous 

 memoir. 



One remark is necessary here. My object throughout had been 

 more especially to determine the nature of the tubercles and of the 

 organism which infests them : the further and larger question as to 

 their function or influence in the economy of the Leguminous plant 

 has been kept subordinate for the present, because I am convinced 

 that more time and appliances are necessary for its complete solution 

 than are at my disposal at present. At the same time some of the 

 following results ought to help in solving the problem as to the 

 possible relations of the tubercle organism to the acquirement of 

 nitrogen by the higher plant. 



During the spring and summer of 1888 I made numerous experi- 

 ments with water-cultures with beans, allowed to germinate in soil so 

 as to be infected by the " germs " therein as demonstrated previously. 

 Several dozens of such cultures were made, and some of them placed 

 in the dark, others in the ordinary light of the laboratory, and some 

 in a well-lighted greenhouse. Tables were prepared showing the 

 number of leaves, living and dead, the condition of the roots, the 

 height of the stem, and so forth, as recorded every week or so (or at 

 shorter intervals) when I examined the plants. It resulted that when 

 the beans are in any way so interfered with that they do not assimi- 

 late more material than is necessary for the growth and immediate 

 requirements of the plant, the infecting organism either gains no 

 hold at all on the roots, or it forms only small tubercles which are 

 found to be very poor in " bacteroids :" in some cases the starving 

 plants began to develop tubercles, which never became larger, and in 

 which the infecting organism seemed to be in abeyance. Whether 

 this is due to the bacteroids being developed in small quantities, or 

 to their absorption into the plant is still a question. 



I hardened many of these tubercles in picric acid, stained them, 



