THE AUSTRALIAN NATURALIST. 67 
show marked differentiation of SLATES similar in outward 
form to stems and leaves. 
Sea weeds can be divided into three zones, according to 
their habitat. (1) The green sea weeds in the upper area of 
the tidal strand; (2) brown sea weeds lower down, and (3) red 
sea weeds in the lower reaches. Of course there is no strict 
demarcation between the zones, for the brown bead-sea weed 
(ZZormosira) is found in the highest rock pools. 
The “giant” forms of BNNs are found among the brown 
sea weeds. 
I will take Phyllospora comosa (Plate 1) as a type. Harvey, 
in “Phyeologia Australica,” gives a general description of this 
Alga, and records that it is found only in the South Seas. - 
Morphological Structures—The Hold fast (Plate I. Fig. 
1. a.) or so ealled roots. This is formed of a number of short 
root-like - processes which become very strongly attached to the 
medium on which the plant is to live. Dr. Bower records of 
Fucus, the growth and fusion of a number of slender filaments, 
each of which becomes attached separately to the rock, ete., and 
then fuse later to form one of the strong root-like branches of 
the hold fast. 
Next is the basal stem structure (Plate I. Fig. 1. b.) which 
is thick, tough and almost round in cross section; it divides later 
into flatter branches bearing leaf-like appendages. Dr. Bower 
records of Fucus that the stems are developed from- the leaf- 
like, first growth of the thallus, by the rapid growth of the 
central mid-rib part, while in the flatter edges, growth ceases 
and in time the mid-rib area becomes thick and strong, while 
the thinner peripheral zone is worn off, and this can be observed 
in Phyllospora. Some of the leaf-like appendages are modified 
to form “fruiting leaves” (Plate I. Fig. 4.) bearing, on separate 
plants, male or female reproductive organs. Other branches 
are completely modified to form large elliptical hollow “floats” 
(Plate I. Fig. 1. ¢.). This dividing up and modifying of the 
general thallus shows a successful development enabling the 
plant to spread out and float in the water so that the light needed 
for all its energies can be obtained. 
Light plays an important part in the development of plants 
and is necessary for all self-supporting plants. For the energy 
yielded by light rays entering certain cells is used to make 
the green pigment Chlorophyll: then this pigment has the 
power to arrest additional - rays of light and this captured 
energy is used for the physiological processes of the plant, the 
