TRANSACTIONS OF SECTION K. 587 
(c) tuberculose. The majority of spores are smooth. Amongst the Agaricaces, 
whilst occasional genera are principally characterised by echinately warty spores 
(e.g., Russula), in other genera they are rare (e.g., occasional in Znocybe). In the 
Polyporavee occasional species of Boletus show this form; in the Thelephoracezx, 
sometimes in Z’helephora (usually more twberculose) ; and in the Gasteromycetes 
they are common. The occurrence of peculiar nodulose or tuberculose spores 
in species of Z'helephora, Inocybe, and several genera of pink-spored Agarics is 
surely more than a coincidence, indicating almost certainly a common ancestry. 
The paucity of species showing this character suggests its presence being a 
handicap to the maintenance of the species. 
(4) Shape.—This may be (a) spherical, (b) somewhat pear-shaped (Lepiota 
type), (c) ellipsoid, (d) elongated ellipsoid, (e) fusiform ellipsoid (mummy- 
shape), (/) curved, and other modifications. (a) Amanita and Amanitopsis fre- 
quently show spherical or subspherical spores. (b) The pear-shaped Lepiota 
type is seen also in Pholiota and Psalliota, all ringed species macroscopically 
resembling each other, widely separated artificially by the colour of the spore- 
mass. The shape of the spores supports the general structure in indicating 
close generic affinities. (c) Ellipsoid—the most prevalent type amongst Agarics. 
(d) Elongated ellipsoid—appearing more in Polyporacee and Thelephoracee. 
(e) Fusiform ellipsoid—characteristic especially of Boletus and perhaps of 
mechanical advantage in the falling of a long spore vertically down a narrow 
tube. 
7. Potato Scab and its Causes. By Professor T. Jounson, D.Sc. 
An account was given of ‘powdery’ scab, due to Spongospora subterranea; 
of black scab, due to Chrysophlyctis (Synchytrium) endobiotica; and of some 
experiments to determine to what extent ordinary scab is caused by mechanical 
irritation. 
WEDNESDAY, AUGUST 26. 
The following Papers were read :— 
1. Inheritance in certain Giant Races of Primula sinensis.* 
By R. P. Grecory, M.A. 
Experiments have been made with two giant races of Primula sinensis, which 
have been shown to be in the tetraploid condition; that is to say, the plants 
have 4x (48) chromosomes in the somatic cells and 2x (24) chromosomes in the 
gametic cells, whereas in the ordinary (diploid) races of the species the numbers 
are 2x (24) and x (12) respectively. One of these races originated in the course 
of my own experiments from plants obtained in the F2 from a cross between 
two ordinary diploid races; the other giant race consists of the progeny of a 
plant very kindly given me by Messrs. Sutton & Sons. 
The result of most general interest, which has been obtained from these 
experiments, is the discovery that the reduplication of the chromosomes has been 
accompanied by a reduplication of the series of factors. In the pure-bred diploid 
race each factor is represented twice, AA; in the tetraploid race it is repre- 
sented four times, AAAA, and there are three distinct hybrid types, namely, 
AAAa, AAaa, Aaaa. These three hybrid types may, or may not, be identical in 
appearance, according as the presence of a single ‘ dose’ of the factor is sufficient 
or insufficient for the perfect development of the character in the zygote; in either 
case they can be recognised by the progeny to which they give rise as a result 
of self-fertilisation. The hybrid AAAa gives no pure recessive types among its 
immediate progeny, but some of its offspring will give pure recessives in subse- 
1 A report of this work has been published in the Proc. Roy. Soc., B, 
vol. lxxxvii., 1914, under the title ‘On the Genetics of Tetraploid Plants in 
Primula sinensis.’ 
