TRANSACTIONS OF SECTION K. 813 
in opposite pairs, each pair at right angles to those above and below, as, for instance, 
in the dead nettle, the strain of the wind would be mainly in two directions, and 
the ‘double girder’ (fig. 2) would be the best form. Ifso we should expect to 
find quadrangular stems associated with opposite leaves. The author then took 
the British flora, and showed that plants with quadrangular stems always have 
opposite leaves, and that plants with opposite leaves have generally, though with 
exceptions, quadrangular stems. The reasons for these exceptions were then 
considered. 
Passing to triangular stems, it was pointed out that they might be accounted for 
by the same considerations. Many Monocotyledons, but not all, have the leaves in 
threes. Sedges, for instance, all have more or less triangular stems, while in 
Fig, 1. Fig. 2. 
grasses they are round. Now, sedges have leaves in threes, while in grasses they 
are distichous, z.e. in two rows or ranks, 
In plants with pentagonal stems the same relation prevails. The bramble, for 
instance, has a stem more or less pentagonal, and the leaves are in whorls of fives, 
a character, as he incidentally observed, which throws light on the number of 
petals and sepals. The petals represent a whorl of leaves, and asarule, when the 
whorl consists of five leaves, the flower has five petals and five sepals; while when 
the leaves are opposite a whorl would consist of four leaves, as, for instance, in 
veronica, where also there are four petals. 
Thus, then, the author finally remarked, plants have worked out for themselves, 
millions of years ago, principles of construction so as to secure the greatest 
strength with the least expenditure of materials, which have been gradually 
pupled to the construction of buildings by the skill and science of our architects 
and engineers, 
2. On Recent Researches on Parasitic Fungi. 
By Professor H. Marsuati Warp, /.2.S. 
3. On the Vegetative Life of some Uridiner. 
By Professor Jako Eriksson. 
4. On the Development of the Aicidium of Uromyces Pox, and on the Life- 
History of Puccinia Malvacearum. By V. H. Burackman and Miss 
Hexen C, I. Fraser. 
TUESDAY, AUGUST 23. 
The following Papers were read :— 
1. Sunshine and CO,-Assimilation : an Account of Experimental 
Researches. By Dr. F, F. Buackman and Miss Marrnaet. 
