28 The Botanical Gazette. - ; (January, 
similar structures in ordinary roots and rootlets. Also the 
cytoplasm of tubercular cells is more granular, that is, it 
contains larger and more prominent dermatosomes, espec- 
ially the palisade cells. It is very likely that whenever a cer- 
tain amount of rhizobia and bacteria have infected the apical 
area of a certain rootlet, their irritating presence produces 
increased metabolism and rapid branching. Thus the in- 
creased number and size of the dermatosomes would be due 
to the rhizobia. . 
The question of the symbiotic relation of Cycas, alge and 
rhizobia is very interesting sand apparently rather complex. 
All soils, especially green house soils, contain rhizobia and 
other bacteria besides numerous alge. These alge are very 
common both in the soil and the vessels in which green house 
plants are grown. That they play an important part in 
binding the free nitrogen of the air has been conclusively 
shown by B. Frank. In examining carpellary and the rudi- 
mentary hypsophyllary leaves of Cycas it was seen that they 
often had a greenish coating consisting of alge. The follow- 
ing genera were noted: Protococcus, Navicula, Chroococcus, — 
Oscillaria, Gloeocapsa, Ulothrix, Chlceosporium and Nostot. — 
Numerous rhizobia, bacteria and several species of hyphal 
fungi were also found. Among the rhizobia I could readily 
recognize Rhizobium mutabile,? Rhizobtum curvum, and Rhiz- 
obium Frankii beside many, to me unknown, species of ba¢- 
teria and cocci. Examination of the surface soil in which | 
the plant grew showed a similar protophytic flora though in 
somewhat lesser abundance. The predominating types among 
the alge seemed to be Protococcus and Nostoc. Among the 
rhizobia and bacteria I could find no predominating type. 
Cross sections of tubercles showed that no algz are inside 
the cells, while nearly all of them, especially those of the 
dermal layer, contained more or less rhizobia and bacteria: 
Parenchyma cells and bast cells of vascular system contain ee 
some rhizobia and bacteria. They seemed to be quite abut 
dant in the apical area. Culture experiments developed three 
predominating types; a coccus, a probable rhizobium © — 
semblimg Rhizobium Frankii, anda larger Indian club shape@ 
bacterium resembling somewhat Rhizobium mutabile of Trifor 
zum repens though smaller and of a more constant size ane 
form (plate Iv, figs. 6, 8). i. 
*Bull. Torr. Bot. Club. 19: 203. July, 1892. 
