138 INTERESTING CASE OF INSECT MUTUALISM. 



One day I was making a rotnid of visits, and left the carriage 

 with my native boy while I made a call. It was a very hot 

 afternoon, such as are common in Durban (Natal) in summer. 

 On my return to the road, after my visit, I found the boy had 

 thoughtfully moved the carriage some distance along to take 

 advantage of the shade of a large " flat crown " tree. The boy 

 was standing at the horse's head half asleep. On reaching the 

 carriage, I found an interesting condition of affairs. The tree 

 had been " weeping " in consequence of several parties of frog- 

 hoppers inhabiting the branches. The cushions, splash-boards, 

 and floor of the conveyance were so w'ct that there had to be a 

 general clean-up before I could go on my way. A tree in the 

 Parsonage grounds began one day to " weep." Wishing to make 

 some observations, I set a vessel upon the ground where drops 

 were falling. As the tree was a high one, and the drops had 

 to fall from a considerable height, and the wind sometimes 

 swayed the branch, all the drops did not fall into the receptacle, 

 but after several hours I poured out the liquid which had been 

 caught, and found that it measured a full quart ; the liquid was 

 as dear as water, and of course consisted of the sap of the 

 tree, which had passed through the bodies of the insects. The 

 small amount of nutritive matter dissolved in the sap had been 

 retained in the bodies of the frog-hoppers, and the clear liquid, 

 slightly viscid, had been expelled. Five or six dozen of these 

 sap-suckers will fill a quart vessel in an hour and a half. The 

 most wonderful example I have as yet met with, as to the quan- 

 tity of liquid shed from a single company or batch of frog- 

 hoppers, came under my notice one very hot summer in Durban. 

 Out walking one day, I noticed a tree " w^eeping." The tree 

 is known as a "flat crown" (Albissia fastigiata). One branch 

 of this tree overhung the road. The groimd had a gentle slope, 

 so that when the liquid fell it was possible, if it fell in sufificient 

 quantities, to saturate the dry, hard, hot ground and then trickle 

 down the incline. Now, althouu'h evaporation was being carried 

 on to a great extent owing to the heat of the sun, the sap shed 

 from the tree, after passing through the bodies of the sap- 

 suckers, had saturated the ground and had made the road so 

 soft that the wheels of passing carts had churned up a miniature 

 swamp, or mud-patch, some five feet wide, with sap standing 

 like water after rain in the depressions made by the cart-wheels. 

 Nor was this all, for the sap was making its way down the 

 incline of the road just as a tiny spring of water would do. 

 I visited this tree two days after I had found it, and took with 

 me my camera and tape measure. I took two good pictures, 

 which I still have in my records, and measured the " swamp." 

 In its broadest part it was five feet, and in a narrow course 

 down the road it extended thirty-five "feet. Considering the 

 dryness of the surrounding ground and the heat of the sun, I 

 was surprised at the quantity of sap which must have been 

 pumped out of that one branch of the tree. The froth manu- 

 factured by these insects is no doubt to some extent a protection 



