794 ANNUAL REPOllT OF THE OfE. Doc. 



has beeu found to retain its vitality for five years. No fungicides 

 have been found strong enough to entirely rid the soil of its presence, 

 as there is always enough left in the soil to start the disease on the 

 next cotton crop. For greenhouse purposes the soil may be sterilized 

 with steam at 130 to 14U pounds pressure when every germ of all 

 fungi would be killed, and weed-seeds also, which would be a de- 

 cided advantage. Some growers have thought that there is a pos- 

 sibility of the soil losing some of its fertility when sterilized, but the 

 Professor stated that in some experiments with sterilizing soil for 

 Violets no injury at all w'as apparent, instead the Violet plants grew 

 entirely too rapidly. It is of course, for greenhouse purposes, that 

 the sterilizing of soil is at all practicable. Some of our expert rose 

 growers make a practice of systematically sterilizing all the soil used 

 in their rose-growing operations, and they are prepared to prove that 

 it pays to do so. Some soils, it is believed, contain more nematodes, 

 or eel worms, than do others, and it is for the purpose of killing 

 this troublesome little microscopic fellow in the soil that sterilizing 

 is practiced for roses. 



A disease called "Black Rust," but entirely distinct from that af- 

 fecting Carnations, alTects some greenhouse plants. Heliotrope and 

 Verbenas, especially. The leaves affected show dark blotches, which 

 in bad cases causes the leaves to become more or less crippled. Black 

 Rust is believed to be caused by one of the mite-insects, which re- 

 •luire a strong microscope to detect. There is hardly any cure for 

 this disease when in an advanced stage, and it is better to destroy 

 the plants so affected entirely and start anew with clean, healthy 

 stock. Stunted, half starved plants are the first, and generally the 

 only ones, to take this disease, so that to avoid it, generous treat- 

 ment is the one greaj: thing needful to keep the plants healthy. 



There are other diseases affecting plants, but those mentioned are 

 the most troublesome, and in order to be sure that everything is be- 

 ing done that can be to avoid diseases in plants, cleanliness in 

 every department in the greenhouse must be the watchword, and 

 ought to be rigidly enforced; and it must be here emphasized that the 

 various fungicides should only be depended upon as preventives, 

 and not cures. 



INSECTS. 



The insect w'hich bothers plant-life in greenhouses most, or in the 

 greatest number, and at the same time the easiest to get rid of, 

 is the ^'green fly," or plant-louse, one of the numerous species of aphis 

 which has the power of reproduction to an extraordinary degree — 

 too prolific almost to be fully realized. 



