Vol. 5 No 7 



TORRl^YA mPARv 



NEW YO;?K 



I^ly' '905 BOfANfCAL 



AN i:x AMPLE OF coMiM.i-x 1 .11" i:-ri:lationship 



i;v Air.KKr SniNKiDKK 



The plant as well as llic animal kin^^doni [)rcscnts numerous • 

 very intcrcstinij^ and complex life-relationships whicli the biolo- 

 gist recofjnizes as synibioses, the naturalist as striu^gle for exist- 

 ence, and the socialist, if he is scientifically inclined, as competi- 

 tion. 



A somewhat remarkable instance of symbiosis has recently 

 come under my observation. Durini^ the vacation months ( May, 

 June, and early July) of 1904, my liltlc daughter and myself 

 were in the habit of taking short morning rambles in the vicinity 

 of our Berkeley home. On Hillegass Avenue near Dwight Way, 

 we noted a row of hawthorns [Cra/acgiis Oxyacaiifha), about 

 twelve feet high. Most of the plants were well infested with 

 plant-lice [Aphis Cratacgi) at this time of the year (June). 

 These pests were found most abundant on the under surface of 

 the leaves and on the young terminal branches and buds, and 

 wherever the bark was unusually thin, injured or abraided ; that 

 is, in places where the cell sap was most readily obtainable. 

 Upon closer examination, it was found that some of the plant- 

 lice were of a black color, due to a fungus attacking them. The 

 remarkable feature was that the parasitized plant-hce seemed, at 

 first, to be quite uniformly distributed among the green healthy 

 individuals. Gradually the fungus disease spread, until perhaps 

 one-third to one-half of all the i)lant-lice on one particular haw- 

 thorn were blackened, but not dead. Many were no doubt 

 killed and fell to the ground. A thin scattering stream of ants 

 (the honey ant, Mvnnicocystis mc/Iigcr) was continuously moving 

 u[) and down the trunk and branches of the hawthorns. The 

 ants visited the Aphis and took from them the sweet secretion 

 (honeydew) found in the posterior glands. Occasionally an ant 

 [No. 6, \'ol. 5, of '1\)RKK.VA, coinprisiiifi jxiges 99-liS, was issued June 24, 1905. J 



110 



