No, 6. DErARTMEVT OF AGRICULTURE. 499 



land has shown that most of the insect's feeding before it enters the 

 apjde is done in the calyx cavity between the calyx lobes, where from 

 75 to 90 per cent, of the worms go in. It is important, therefore, to 

 have the calyx cavity well charged with poison. Formerly it was 

 supposed that this could be accomplished at any time before the 

 young fruits turned down. Slingerlaud* has pointed out the fact 

 that the caljx lobes of the young apples close over the cavity in from 

 seven to ten days after the blossoms fall. (See Plate I.) After such 

 closing, it is practically impossible to get the poison into the cavity. 

 The importance, then, of completing the application before the clos- 

 ing takes place is emphasized. To the owners of large orchards this 

 is eispecially important, for it means that sufficient apparatus must 

 bo provided to enable the spraying of the entire place before the ex- 

 piration of the period mentioned. So it is also with the great ma- 

 jority of fungous diseases: It is impossible to reach them when 

 once they have penetrated the skin, as will be explained later. 



General Classes of Mixtures. 



There are two general classes of spray mixtures, viz: 

 1 Insecticides. 

 2. Fungicides. 

 The first class includes all mixtures used for the destruction of in- 

 sect pests; the second includes all applied against fungous diseases. 



Classes of Insects. 



Every fruit-growler or farmer knows what an insect is. But not 

 every fruit-grower or farmer knows that the insects attacking fruits 

 and plants are of two general kinds They are; and the two classes 

 are as follows: 



1. Chewing insects, or those which have biting and chewing 

 mouth-parts. These take in and digest solid food, usually the leaves 

 or fruit of plants. Such are, for example, the codling moth, canker 

 worm, web worm, tent caterpillar, leaf skeletonizer and the like. 



2. Sucking insects, or those w'hich have sucking mouth-parts. 

 These suck the juices of the plant and therefore live entirely upon 

 liquid food. These are the plant lice, scale insects and the like. 



Naturally, then, the life habits of these classes of insects demand 

 very different methods of sprajang in order to destroy them. The 

 first class can be reached through their food supply, and are, there- 

 fore, easily destroyed by poison eaten along with the parts of the 

 plant attacked. The second class cannot be reached through their 

 food supply, as they derive their sustenance by sucking the juices 

 from within the plant tissues. They can, therefore, be destroyed 

 only by contact with some caustic or suffocating compound. There 

 are, therefore, two classes of insecticidal sprays: 



•Cornell University Experiment Station Bulletin 142, pp. B4 and 65. 



