64 
paid this time the grubs hatched out of this root gall form the 
wingless fly, which again crawls along the twig to make the 
oak apple. A wonderful instance of what is known as the alterna¬ 
tion of generations. 
There are twenty different kinds of gall forming insects on the 
oak alone. But the interesting part to us to-night is that certain 
fungi cause galls on plants and trees, the mere presence of these 
fungi, or chemical agents secreted by them seems to stimulate the 
cells of the host to become hypertrophied, and this may be either in 
a localized form, as in the bladder plum, or where the mycelium 
spreads along the twigs to cause what you all know as “ witches’ 
brooms.” 
Floral malformations occur when a fungus gall attacks the 
reproductive or flowering portion of a plant. 
Irwin F. Smith, Pathologist at the Rockefeller Institute in 
New York, supplies us with some curious facts in connection with 
“ crown galls ” in the Paris Daisy, a kind of marguerite. He 
calls it plant cancer, and states that it is exactly w r hat a malignant 
tumour of a plant might be exepected to be. The tumour is non- 
capsulate, its growth is peripheral, and it has a well developed 
stroma, consisting of vessels and fibres. 
Secondary tumours develope, and these have a strong 
tendency to take on the structure of the part they affect, thus 
a stem tumour may appear in the leaves, but is composed, in 
great part, of the descendants of the originally infected stem cells. 
A bacterium ( tumefaciens ) has been isolated by him in pure culture, 
and some success has been obtained in inoculating fish with it. 
We spoke of how we are to protect ourselves against the 
ravages of these minute fungi. 
Let us look, in conclusion, how we are to protect our plants. 
Here, again, a wide cleanliness is what must be aimed at, young 
seedlings suffer most, therefore have your greenhouse light and 
well aired, and so arranged that you can turn a hose on it, white¬ 
wash often, and have your benches of slate often cleansed^ or if 
they are of wood, cover them with ashes, which, having come from 
the fire, are sterile. Boil your flower pots and sterilise the soil or 
see that it is clean.* If you have a rose bed near fir trees, creosote 
or tar the trees, and, similarly, If you cut off a branch of a fir, 
tar or creosote the cut surface. I don’t believe much in spray¬ 
ing with chemicals; prevention is better than cure. 
The lecture was illustrated by diagrams, pictures and colour photographs 
.(Lumiere’s process), as well as tube cultures from animal and vegetable tissues. 
