==Leaf Spot of Celery.==—­This disease, which is caused by a minute fungus (=Septoria apii=, Chester), is capable of inflicting serious damage to the Celery crop unless prompt measures are taken to exterminate it.  The first sign of its appearance is to be found in the leaves in the form of small brown patches.  These are, however, quite distinct from the spots deficient of leaf-green due to the attack of the Celery Fly larvae, and on close examination may be recognised by the presence of a number of very small black points.  From the leaves the fungus quickly spreads over the leaf-stalks and finally to the heart of the plant, ending in its total collapse.  So rapid is the multiplication of the spores, especially in moist weather, that a few diseased plants are capable of infecting a large plot within two or three weeks.  Immediately discoloration of a leaf is noticed the affected portion of the plant should be picked off.  If the stage of the disease is so far advanced that the outer leaf-stalks have become decayed, the entire plant should be removed and destroyed.  It is of the utmost importance that every particle of diseased material be consigned to the fire and not to the waste heap.  Spraying three or four times with Bordeaux mixture at intervals of two or three weeks may be helpful in the case of a light attack, but the safest course always is to remove and destroy any plant on which the fungus is found.  One of the most frequent means of introducing Leaf Spot of Celery is through the use of infected seed, and therefore only seed which has been treated for the destruction of the fungus should be sown.

==Lettuce Mildew.==—­This fungus is named =Bremia lactucae=, formerly known as =Peronospora ganglioniformis=, and is sometimes of the most destructive character.  It covers Lettuce leaves with a fine white bloom, which decomposes the leaves, and makes them adhere together in one putrescent mass.  It should be looked for in its earliest stages, and be hand-picked and burned.  Old Lettuce stumps should likewise be pulled and burned, otherwise they may harbour the disease.

==Onion Mildew== is caused by the fungus =Peronospora Schleideni=, which is occasionally disastrous in its effects, more especially in cold, wet seasons.  It occurs at uncertain intervals of time with extraordinary virulence, and then utterly destroys the crops.  Autumn sowing is considered a good preventive by many growers, as the disease is frequently fatal to spring seedlings.  In its early stages the mildew may be successfully dealt with by freely dusting the plants with flowers of sulphur when wet with dew, or by the application of sulphide of potassium in the proportion of one ounce to a gallon of water.  Otherwise all diseased material should be removed and burned.