TRANSACTIONS OF SECTION K. 693 
presence of colour in the stem which is found to hold good also in the case of 
plants of other races than those just described. Whether this coupling is simply 
zygotic or whether it may sometimes be gametic is not yet clear. 
6. The Phylogenetic Connexions of the recent Addition to the Thread 
Bacteria (Spirophyllum ferrugineum [Z//is]). By Davip Exis. 
This new species, discovered in the iron-waters of Renfrewshire, and since 
found to be fairly well distributed throughout the west of Scotland, is phylo- 
genetically interesting because it links the iron-bacteria with the genus Spiromonas, 
which has hitherto been thrust out of the bacteria-group, but inserted in Migula’s 
classification as a dependent. Spirophyllum agrees with Spiromonas in possessing 
a flattened body thickened at the edge in the same way. Both are also spirally 
twisted, but whereas Spiromonas never shows more than one and a quarter turns, 
and is motile in the mature condition, Spirophyllum may exhibit any number of 
turns, and is only slightly motile immediately subsequent to germination, Whilst 
the relationship between these two genera is undoubted, it is equally certain that 
the new genus Spirophyllum is very closely allied to the other iron-bacteria on 
account of the similarity in their mode of life, their mode of deposition of iron, 
and more especially in their mode of reproduction. It therefore seems desirable 
to alter slightly the definition of the order Chlamydo-bacteriaceee (Migula’s 
classification), so as to include koth Spiromonas and Spirophyllum. This could be 
done by inserting ‘cylindrical or flat cells, usually surrounded by a limiting 
membrane,’ instead of ‘cylindrical cells, arranged in threads, and surrounded by 
a limiting membrane.’ 
7. The Structure of Root Tubercles in Leguminous and other Plants. 
By Professor W. B. Borromuey. 
The root-tubercles in all leguminous plants examined appear to arise endo- 
genously from the cortical cells just outside the endodermis of the root. These 
cells are stimulated by the ‘infection thread,’ which grows almost straight from 
the infected root-hair towards the vascular cylinder of the root, and a conical mass 
of cells develops which forms the young tubercle. Vascular strands are developed 
in the cortex of the tubercle, but there is no central strand of conducting tissue, 
and nothing comparable with a root-cap covering the end of the tubercle. In fully 
developed tubercles the ‘ bacteroid’ tissue is situated entirely within the vascular 
strands—intrafascicular. 
The root-tubercles of Alnus, Eleagnus, and Cycas are morphologically lateral 
roots, showing a central vascular cylinder, with a well-marked endodermis, com- 
pletely surrounded by ‘ bacteroid’ tissue—eatrafascicular. These tubercles branch 
dichotomously, and are perennial, thus differing from leguminous tubercles, which 
are of limited growth, 
8. Cell Division in Merismopedia glauca. By B. H. Bentiny. 
Eaeh cell is ovoid in form, with its long axis perpendicular to the surface 
of the colony. It contains a ‘central body’ which appears to consist of two 
spiral threads. During cell division each thread becomes wider and undergoes 
longitudinal fission, Two of the four threads pass into each daughter cell, No 
breaking of the threads into short segments was seen. 
