ESSAYS. 25 
Paraffin was melted and poured into a cast, the grain placed in the liquid 
paraffin, and the whole, after it had got thoroughly cool and hard, fitted into the 
section-cutter. Transverse and longitudinal sections, of a thickness varying 
from 0.01 to 0.06 millimeters. were made and placed in turpentine, the latter 
dissolving the paraffin in a short time. From thence the sections were mounted 
in Canada balsam. 
Wheat has a thin regular coating, consisting of the hard epidermis and a 
layer of albuminous cells on the inner side, containing oil-drops. The mounted 
specimens do not show the oil, it having been dissolved by the alcohol and tur- 
pentine. These outer cells are of a brown colour. The endosperm. the only 
part of the grain which contains starch, consists of large polyhedral cells, tilled 
with minute starch grains. 
In examining the barleys, Cape barley is found to have a coarser skin and 
more oil, and the albuminous cells are very much larger. In the Golden Melon, 
the starch granules are spherical ; in the Cape barley, on the other hand, they 
appear oblong. 
In oats the epidermis is very thin, the albuminous cells are of a peculiar 
shape, and the starch granules are larger. 
In rye the epidermis is still thinner, there is no oil in the outer layer of 
cells, and the starch grains are larger than those of wheat and barley. 
VI.—Norss on Rust (Puccinia graminis).—By T. W. Bune. 
The rust which occurs on wheat in Kurope is produced from a fungus found 
on the leaf of the Barberry tree, which is known by the "name of Puccinia 
graminis. This fungus passes through different stages. 
On the Barberry leaf it forms the so-called cluster cups, which give off an 
immense number of spores. These spores cannot develop again on the leaf of the 
Barberry ; but if carried by the wind on to wheat-plants, or other cereals, they 
commence germinating by giving off a germ tube, which enters the leaf or stem as 
the case may be, and ir the course of 6 or § days develop into an elongate red 
mass in the parenchyma of the leaf. As this increases in size, the epidermis of 
the leaf at last bursts, and reddish looking spores are exposed, forming rust. 
This forms the second stage of Puccinia graminis. These spores are blown on 
to other cereal plants and develop rust again, and this process goes on till the 
autumn. At that time of the year the fungus begins to produce spores of a 
different kind, each spore being protected by a wax-like secretion on the outside. 
In this condition the spores are preserved through the winter on the stems of 
Graminez. This forms mildew, the third stage of /Puccinia graminis. 
In spring each cell of the mildew spore develops a short tube, which gives off 
from 2 to 4 slender branches, at the end of which spores are produced. These 
spores do not, in Europe, reproduce mildew, but develop—if carried by tke wind 
on to the Barberry tree—into a fungus on the leaves of that tree. These form 
the cluster cups, or first stage of Puccinia graminis ; thus completing the life cycle 
of the fungus. 
Rust on New Zealand wheats cannot be produced in this manner, as there are 
such a very small number of Barberry trees in the country, and rust is known in 
Australia to occur 500 miles from the nearest Barberry bush. 
It follows from this that in Australia and New Zealand the Barberry must 
be either substituted by another plant, or the rust continues to propagate without 
a change of generation, always remaining in the stage of rust. 
Of the rusts met with in New Zealand nothing is known, so that we cannot 
say which cluster-cup belongs to which rust. A fungus was found on a rush, 
Juncus fusus, and investigated, but it appears hardly likely that it is the cluster- 
cup stage of Puccinia graminis. On the other hand, a rust, resembling Puccinia 
graminis in every respect, was found in the Juncus, producing spores in the 
winter (August, September) on the dead and half dry stems. 
If the growth of this rust is not impeded by the winter, it appears likely 
that the ordinary rust will also grow in New Zealand during the whole year. As 
the alternation of generation in Puccinia graminis has doubtless been caused by 
the severe winter of Europe, it seems quite possible that when this cause is re- 
moved , the effect—the change of generations in the Puccinia graminis—may also 
alter, and by atavism return to the old style of direct propagation. Some species 
of rust do not show any alternation of generation. 
If we merely have, as does not appear unlikely, in the colonial Puccinia 
graminis a case of atavism, it will be of the greatest interest, and | hope that I 
may be able to prove this at some future time, 
