802 Spratt . — The Formation and Physiological Significance of 
and, in 1912, he has shown the nodules of Myrica Gale to be bacterial in 
origin. The author has described the root tubercles of Alnns and 
Elaeagnus as being caused by the infection of the root with a species of 
Pseudomonas radicicola , which afterwards flourishes in the cortical cells of 
the nodule. 
The first part of the present series of investigations was carried out 
with material of Podocarpus To tar a, Podocarpus elongata , and Podocarpus 
chilina obtained from the Royal Botanical Gardens, Kew, at various seasons 
of the year. At the suggestion of Professor Bottomley, however, the 
observations were extended to comprise the whole of the group Podo- 
carpineae ; and through the kindness of the Director of the Royal Botanical 
Gardens, Kew, roots of Microcachrys tetragona , Dacrydium Frank lini , 
Saxegothaea conspictia , and Phyllocladus trichomanoides were obtained. 
In all the genera of the Podocarpineae numerous nodules are present on 
the small roots, along the sides of which they are arranged in two very 
definite rows, thus producing a beaded appearance (PI. LXXVII, Figs. 1-5). 
In the four species of Podocarpus examined, P . Totara , P. elongata , P. chilina , 
and P. alpina , the nodules are almost spherical in shape, attaining a diameter 
of o-8 to 1 mm., and are very symmetrically disposed along the two sides of 
the root (Fig. 1). The nodules are very numerous, occurring quite close to 
one another along the whole length of the roots, which branch relatively 
infrequently. In general appearance the roots of Dacrydium Franklini 
resemble those of Podocarpus , but they branch somewhat more frequently ; 
the nodules are smaller, only attaining a diameter of 0-54 to o-68 mm., and 
although they occur in two rows along the sides of the roots they are less 
regularly arranged (Fig. 2). The roots of Microcachrys tetragona are very 
fibrous, numerous very fine branches being produced, and along two sides 
of all these numerous small rootlets, minute nodules, with a diameter of 
0-25 to 0-35 mm., are arranged side by side in close proximity with one 
another (Fig. 5). In Saxegothaea conspicua the roots present a coralline 
appearance, being quite small, but so repeatedly branched that dense clusters 
are produced, and the roots bear two very closely packed rows of nodules, 
which are 0-4 to 0-5 mm. across (Fig. 3). Phyllocladus trichomanoides has 
a much more straggling root, and the nodules are less numerous than in the 
other genera, but are present upon the small roots, where there are two rows, 
thus presenting the characteristic beaded appearance. In this genus they 
appear to be more widely separated from one another, and attain a diameter 
of about 0*5 mm. (Fig. 4). 
The roots and nodules of all these plants being quite small, it was 
found convenient to mount some of them whole for examination under the 
low power of the microscope, which immediately revealed the fact that the 
nodules in all the genera are endogenous in origin and each possesses 
a small but well-defined vascular strand, which is connected with the root- 
