FAUNA AND FLORA OF MANGROVE SWAMPS
141
his arguments on the fact that they grow in water of quite high salinity
and that the leaves of most mangroves show a degree of succulence in
having water storage tissue in the leaves. He considered the environment to be “ physiologically dry ”. Uphof and also von Faber (p. 35
of his revision of the third edition of Schimper’s “ Pflanzengeographie ”,
1935) regard this assumption as being unjustified.
Mullan (1931a,b, 1932-33) and Walter and Steiner (1936) show that
the stomata of mangroves are not protected and that they are present
on both surfaces of the leaves. According t o von Faber (1935, loc. cit.)
the transpiration rates of both Avicenniu marina and Rhizophoru
mucronata are higher than that of Mungifera indica (the mango tree)
under similar conditions of temperature and humidity. No evidence is
given as to what these conditions were! On the other hand, Walter and
Steiner regard the transpiration rate as being low. I n the species they
studied at Tanga (Tanzania), viz. A . marina, R. mucronatu, S. alba,
C. tagal and L. racenzosa, they recorded values lower than those found
by Stocker (1935) for tropical glycophytes.
More work on this subject appears to be necessary.
The function of the water storage tissue present in the leaves is
unknown. I n Sonnerutia ulba Walter and Steiner record that leaves on
the lower branches have more of it than those on the upper branches.
Figure 40 shows this difference. Uphof argues that, since the water
storage tissue in most mangroves lies between the upper epidermis
and the palisade chlorenchyma, its function may be to filter off heat
rays. On the other hand, its central position in Sonneratia precludes
this.
No work appears to have been done on mangroves equivalent t o
that on the biochemical functions of succulence in various desertic
plants of the family Crassulaceae.
The osmotic pressure of halophytes is normally higher than that of
non-halophytes, but again values given by different workers show much
variation. Taken generally, values given by more recent workers using
kryoscopic methods are lower than those of earlier workers using
plasmolytic methods. Kryoscopic techniques demand a quantity of
fluid. This is normally obtained either by homogenizing several leaves
and then finding the osmotic pressure of the filtrate or by pressing
fluid from leaves. I n either case the contents of all the cells in a leaf
are mixed. It may well be that the contents of the water storage cells
have a lower osmotic pressure than the chlorenchyma which formed tbe
substrate of the plasmolytic observations.
Walter and Steiner (1936) found values around 32 atm for SonrLerutia
alba and Rhizophora mucronata. The soil water showed an osmotic
141
his arguments on the fact that they grow in water of quite high salinity
and that the leaves of most mangroves show a degree of succulence in
having water storage tissue in the leaves. He considered the environment to be “ physiologically dry ”. Uphof and also von Faber (p. 35
of his revision of the third edition of Schimper’s “ Pflanzengeographie ”,
1935) regard this assumption as being unjustified.
Mullan (1931a,b, 1932-33) and Walter and Steiner (1936) show that
the stomata of mangroves are not protected and that they are present
on both surfaces of the leaves. According t o von Faber (1935, loc. cit.)
the transpiration rates of both Avicenniu marina and Rhizophoru
mucronata are higher than that of Mungifera indica (the mango tree)
under similar conditions of temperature and humidity. No evidence is
given as to what these conditions were! On the other hand, Walter and
Steiner regard the transpiration rate as being low. I n the species they
studied at Tanga (Tanzania), viz. A . marina, R. mucronatu, S. alba,
C. tagal and L. racenzosa, they recorded values lower than those found
by Stocker (1935) for tropical glycophytes.
More work on this subject appears to be necessary.
The function of the water storage tissue present in the leaves is
unknown. I n Sonnerutia ulba Walter and Steiner record that leaves on
the lower branches have more of it than those on the upper branches.
Figure 40 shows this difference. Uphof argues that, since the water
storage tissue in most mangroves lies between the upper epidermis
and the palisade chlorenchyma, its function may be to filter off heat
rays. On the other hand, its central position in Sonneratia precludes
this.
No work appears to have been done on mangroves equivalent t o
that on the biochemical functions of succulence in various desertic
plants of the family Crassulaceae.
The osmotic pressure of halophytes is normally higher than that of
non-halophytes, but again values given by different workers show much
variation. Taken generally, values given by more recent workers using
kryoscopic methods are lower than those of earlier workers using
plasmolytic methods. Kryoscopic techniques demand a quantity of
fluid. This is normally obtained either by homogenizing several leaves
and then finding the osmotic pressure of the filtrate or by pressing
fluid from leaves. I n either case the contents of all the cells in a leaf
are mixed. It may well be that the contents of the water storage cells
have a lower osmotic pressure than the chlorenchyma which formed tbe
substrate of the plasmolytic observations.
Walter and Steiner (1936) found values around 32 atm for SonrLerutia
alba and Rhizophora mucronata. The soil water showed an osmotic