Miss G. Lister. 
16 
on the same thallus; so that there appears to he often no sharp 
division of the plant into stem and root. From the structure of 
the flower the order is considered by Professor Warming as probably 
most closely allied to Saxifragaceae; it comprises about 120 
species, which have been grouped under twenty-one genera. They 
are found in the tropical parts of Asia, Africa and America, and 
one genus extends into N. America. 
The genus Tristicha contains, according to the researches of 
Professor Warming, but two species. T. liypnoidcs Spr. occurs in a 
great variety of forms in Central and South America, and South 
and Tropical Africa, including Abyssinia, Madagascar and Mauritius. 
T. alteruifolia Tul., its near ally, has been recorded from Central and 
West Africa and Madagascar. They both have a moss-like habit, 
and the leaves are arranged along the leafy shoots in a more or less 
tristichous order: the small flowers are terminal on short branches, 
and possess a membranous three-lobed perianth, a single stamen, a 
three-celled ovary with free styles, and numerous ovules. T. alter- 
nifolia differs from its ally in having longer narrower leaves, less 
clearly tristichous in arrangement, the flowers often in pairs, and 
capsules on longer pedicels. 
The Egyptian specimens consist of small pieces of the brown 
fleshy creeping thallus, from which arise slender leafy stems 
measuring half to three-quarters of an inch in length. The thallus 
is made up in part of smooth branching lobes that may be regarded 
as roots, although no root-cap is developed; the branches develope 
endogenously, and grow over and about one another, and were firmly 
attached to the rock by numerous clamp-like root hairs. The rest 
of the thallus consists of short flattened creeping stems with small 
scale-like leaves scattered over the sides and dorsal surface ; from the 
sides of these short stems, in the axils of the leaves, the long slender 
stems arise. 
The epidermis of the thallus is composed of small flattened 
rectangular cells, many of which contain plate-like siliceous 
bodies that are characteristic of the family. Beneath this, and 
forming the principal mass of the thallus, is a thick-walled parenchy¬ 
matous tissue, without inter-cellular spaces, richly stored with starch 
granules; siliceous bodies occur here also, and are larger and stouter 
than those of the epidermis; they are rectangular or resemble short 
rods in shape, and show a grooved and pitted surface. They are 
well seen when sections of the thallus have been treated with a 
solution of chromic acid. 
