192 
Spratt. — A Comparative Account of the 
shrubs, herbs, and climbers. Amongst so much diversity one naturally 
looks for differences in the root-nodules of these plants, and they exhibit 
great variation in form and size, and some also in their anatomy. 
From the investigation of a large number of genera it seems possible 
to place them in four groups, thus : 
I. The Genisteae type, in which the nodule is primarily spherical, with 
a spherical meristem outside the bacteroidal tissue, which later becomes 
localized at certain parts, and thus the nodule acquires a very uneven surface 
and shape see (PI. XIII, Fig. 1). The vascular supply forms one broad zone 
across the base of the nodule, which subsequently branches and produces 
a varying number of strands. The bacteroidal tissue becomes separated 
into a number of distinct areas with a varying amount of sterile tissue 
between them (see Text-fig. 2). The nodule is protected by a relatively large 
development from a well-defined phellogen of regular layers of cells, of which 
large areas are repeatedly split off and renewed as the nodule grows (see 
Text-fig. 2. a. Longitudinal section of nodule and root of Lupin, b. Longitudinal section 
of an older nodule, x 20. 
PI. XIII, Fig. 8 ). Infection threads are rarely produced ; in fact, Beijerinck 
says none are formed at all in Lupin. The nuclei with prominent nucleoli 
remain conspicuous for a long time in the bacteroidal cells. 
Plants with this type of nodule are further linked together by being 
woody and having a copious development of periderm ; many are shrubs, 
e. g. Genista , Ulex , Amorpha , and Laburnum is a tree. They can all live 
on poor dry sandy soil, and some where there is little or no calcium 
carbonate, e. g. Lupin. They are further characterized anatomically by 
the presence of schizogenous secretory cavities with tanniniferous contents 
which are colourless in the living plant, but become brown by the action of 
oxidizing agents and drying. Curious four-sided prismatic structures also 
occur in the parenchymatous tissue, which are crystals of calcium oxalate 
and hatfe been called styloids. The medullary rays traverse the secondary 
xylem obliquely, forming a kind of net-like pattern and producing knot- 
like swelling in the neighbourhood of the xylem parenchyma. Tannin 
sacs and styloids also occur in the nodules, and the parenchyma is more 
