THE AUSTRALIAN NATURALIST. 195 
After examining the nodules of several Australian legumes, 
G. P. Darnell-Smith makes the following remarks :—‘‘The 
presence of algae-like cells in the root tubercles, and of green 
colouring matter (chlorophyll?) which has been observed in 
the parenchyma immediately adjoining the point of attach- 
ment of the root-tubercles in lucerne and in clover, suggest 
that we have to do .. . not with a case of symbiosis peculiar to 
that natural order (Leguminosae), but with an example of a 
certain kind of symbiosis, which is common in many other 
natural orders. lichens, Mycorhiza, and Leguminous’ no- 
dules seem to have certain characters in common.”’ _— 
Symbiosis in Cycadaceae. ri 
- Tt would seem that the nodules examined by Darnell-Smith 
are intermediate in character between the simple form of 
symbiosis usually associated with legumes and that found in. 
the Cycadaceae. In these latter plants, Pseudomonas radici- 
cola, occurs in nodule-like structures formed by - distorted 
rootlets. Beneath the surface is the Algal zone, so-called 
from the presence of an alga (Vostoc): Professor Bottomley 
has found that Pseudomonas is always associated, in the spaces 
of the Algal zone, with another bacterium (Azotobacter). 
Experimentally, he claims to have ‘shown, that the nitrogen 
assimilation of the associated bacteria is greater than that of 
the two acting independently. 
In this case four organisms are associated, the cycad 
and the alga, providing carbonaceous food and the 
bacteria combined fixing nitrogen. A.B. Rendle (Classifica- 
tion of Flowering Plants), describes the origin of the cycad 
nodules, ‘‘Bacteria enter at the apical region of the rootlets. 
Rapid swellings follow, and a definite zone of cortical cells is 
disorganised, forming spaces which communicate with the out- 
side air by lenticel-like apertures. These spaces become 
filled with Wostoc, and the adjacent cells of the cortex send > 
papillate prolongations into it.” 
Symbiosis Between Green Plants. 
Here may be mentioned certain curious associations of 
chlorophyll-bearing plants. In Azolla, some liverworts (as 
Anthoceros), Lemna (Duckweed) and Gunnera (one of the 
Haloragidaceae), the two latter flowering plants, the asso- 
ciation is with the alga Wostoc. What 1s the value of this as- 
sociation? Is one member a parasite ? 
Lichens.—In the well-known case of the lichens, the plants, 
which indeed are not plants in the limited sense of the word, 
being formed by the association of an Ascomycete or Basidio= 
mycete fungus with an alga. The alga provides carbonac:: 
