THE ORIGIN OF RUSTS 817 
The general ‘form’ in which the Flora is presented leaves 
nothing to be desired. The book is well printed on good paper, 
ae bound, handy and portable for the use of the field-worker, 
has an excelle nt map. otanist visiting any part of the 
Ceiienial Islands would be sufficiently equipped with it, as, at the 
end of the book, there is a tabulated and comparative mt carefully 
pe i of the plants found in all the islands of the archipelago. 
Fro m a business point of view, it ought to sell well, and should be 
in the hands of all critical students of the British Flora 
Freperic N. Widest 
Tue Oriain or Rusts. 
Proressor Jaxos Eriksson, the distinguished Swedish myco- 
logist, has rede! published, in the Arkiv Siir Botanik K. Svensk 
Vet., a reply to Prof. Marshall Ward’s criticism of his work on the 
origin of ace. Eriksson holds ear the appearance of Rust on 
se coun 
s and othe 
by external infection. Not only in 7 the field, but in carefully pro- 
tected cultures, pvr of rust have grown on the host plant 
where, seemingly, external infection was impossible. He has there- 
fore come to the sSroluates that the disease must be inherent in the 
outbreaks of the disease he has f rd his hypothesis of a 
mycoplasma that lives in symbiotic relationship with the protoplasm 
of the higher plants sea t 
on the host; it is only in specially favourable conditions o 
perature or humidity that it becomes an active and injurious eagome 
forming the well- mage: Uredinee fruits. Eriksson terms this s 
aneous appearance of the rust a case of primary sities: me 
distinguish it froin ‘the sooohtery infection, which is directly due to 
spores. Mycoplasm as yet remains a hypothesis—its author has 
failed to prove it either in the seeds or in the growing plants; he 
hopes, however, that as methods improve 
He sectioned by hand the tissues in the immediate neighbourhood 
of “ primary’ pustules, and he found in the cells bodies, resembling 
the protoplasm of the host, either floating from or attached to the 
e cell; these ies, which he ¢; corpuscles spéciaux, 
grow sth pierce the cell-wall, and become the fungus hyph# of the 
Pucciiéa: and he considers them, in the early stage, to be the ta 
visible appearance of the mycoplasma, — the intermediate fo 
between the mycoplasma and the myceliu 
Marshall Ward has ili attacked a > problem of Rust-infection, 
and he has grown plants susceptible to the disease for the first time 
in completely sterilized conditions from a seed to the mature plant. 
On these plants = has had no instance of fungus growth. el 
