Midge Gall of Myrsine australis — Arnold 
117 
Fig. 4. Detail of Figure 3. v, Vascular strand; cn, chlorophyllous nutritive tissue; c, larval cavity; e, epi- 
dermis of gall. 
projecting inwards. The concave base of the 
cavity is composed of chlorophyllous nutritive 
parenchyma (Fig. 3) which continues to multi- 
ply as the larvae feed. This growth ceases soon 
after the larvae discontinue feeding. 
No remnant is left of the shoot apical meri- 
stem which originally gave rise to the two or 
three primordial leaves. In the development of 
galls at stem tips, increase in length of the 
branch is therefore curtailed at the same time as 
the leaf primordia are converted, under the in- 
fluence of the larvae, into a gall. 
The internal anatomy of the gall is rather 
more stemlike than leaflike, lacking as it does 
the characteristic stomatal arrangement and 
associated organisation of palisade layers and 
spongy mesophyll. 
A very prominent cuticle extends over the 
gall epidermis and is continuous with the 
equally thick cuticle of the normal epidermis 
of the supporting stem. 
Apart from the nutritive tissue surrounding 
the larvae, the histological features of the galls 
are the same as are found in the normal stem, 
namely: red pigmented cells, secretory cells, 
schizogenous cavities and canals with yellow or 
reddish brown contents, and normal vascular 
tissue (Metcalfe and Chalk, 1950). 
DISCUSSION 
A study of the life cycle of the gall midge 
was not undertaken, and the record of emer- 
gence of adult flies in autumn in the laboratory 
appears to be unseasonal, and related to higher 
average temperatures than those prevailing out 
of doors. 
It would seem that the main morphogenetic 
changes accompanying gall formation are a 
suppression of the activity of the marginal 
meristems of the leaf primordia togteher with 
the eventual destruction of the shoot apical 
meristem from which the leaf primordia arose. 
There is evidence of limited growth of the leaf 
apex. 
The bulk of the tissue appears to be con- 
