422 



The Weekly Florists' Review. 



Febkuaky 28, 1901. 



Bacteria require a good deal of moisture 

 to develop well. It was therefore a very 

 proper recommendation to keep the foli- 

 age as dry as possible and give the plan'ts 

 plenty of light and air. This practice 

 w^as said to be followed as a rule by very 

 beneficial results to the health and vigor 

 of the plants, especially when aphides 

 were kept dowir as they were also sup- 

 posed to introduce the germs of the dis- 

 ease into the tissues by their punctures. 

 It had been noticed that where these in- 

 sects were numerous the disease was bud. 



■.-Cu:;^£isjE^, 



Pig-. 4. The sucking tube (B)ofau aphU (A. J 

 passing down between the cells of the leaf to the 

 vascular bundle' from which sugar and food arc 

 withdrawn. 



The Carnation in Healtli and Disease. 



Now it happened that a large house of 

 carnations at the U. S. Propagating Gar- 

 dens came down with a malady which 

 answered the description of baeteriosis in 

 every particular. The plants had been 

 fumigated with tobacco in the usual way 

 to keep down aphides and the foliage 

 had been kept comparatively dry to guard 

 against disease in general. Attempts 

 were made to check the trouble by spray- 

 ing the young foliage of some of the 

 plants several times a week with germi- 

 cidal solutions such is corrosive sublimate 

 and formalin, but none of these appeared 

 to do any good. It was therefore decided 

 to force the plants as rapidly as possi- 

 ble, and get what flowers we could from 

 them; the temperature was raised a 

 little above the rinrnial .iiid the plants 

 were frequeiill\ -niirjrd. To our sur- 

 prise, in the iii..i-ir imH, fi-oquoirt 



syringings thr ]il;mls ur.ally improved 

 and showed less of the disease. The 

 experience led us to examine very care- 

 fully the bacterial theory of the trouble. 



A great many sections were cut 

 through diseased spots of all sizes and 

 ages and many tests for bacteria were 

 made. The peculiar bodies which were 

 formerly thought to be bacteria were 

 finally shown to be the products of the 

 disorganizing cells. But why should the 

 cells disorganrize in such a peculiar pro- 

 gressive manner? Although bacteria 

 could not be demonstrated with the mic- 

 roscope they might still be present under 

 some peculiar condition. It was neces- 

 sary to examine the diseased and healthy 

 tissues by the so-called culture method, 

 that is, as I have previously explained, 

 to put some of the tissue in question, 

 without contaminating it in any way 

 from outside, into dilute meat or vegeta- 

 ble broths or on sterilized potato or gela- 

 tine. If bacteria arc present they soon 

 become apparent by their very rapid de- 

 velopment under these conditions. 



Diseased plants were obtained for this 

 purpose from most of the large carnation 

 cen-ters of the country through growers 

 familiar with the disease. The yellow 

 germ supposed to be the cause of the 

 disease was found in several cases but 

 never in the inner tissues of the plant. 

 In fact in nearly all cases no bacteria 

 or fungi of any "kind were found in the 

 diseased spots of the leaves. Occasion- 

 ally in the last stages of the disease when 

 the surface of the spot had begun to 

 break down, bacteria and fungi of various 

 kinds were found in the tissues. It w^as 

 evident tlin . f,.i,- ili.ii these could not 

 be the can-, .-i iln .li-ra-,,-. 



llowevci. 1m iii:iIm -hit. ;i large amount 

 of healthy yuw^ ■^v<\\\\\ of many plants 

 free from in.si'ct or utlior iirjury of any 

 kind was inoculated with the germ said 

 to cause the disease but no cases of in- 

 fection woip .:litaiiicil. Other bacteria 

 found on tlir -uif.or df the leaves were 

 tested in Ih.- ~:i\\ir wax. Ijut no bacteria 

 were fouii.l Ihal |..n,lii,rd any kind of 

 disease oitluT wlim ilimwnjhiv washed 

 over the voun- \>-.'^" ••> iM-t..l livpo- 

 dennicallv into thr li--ih-_ Ihi. settled 

 the matter of the cau.su ui tliu disease ait 

 far as bacteria were concerned. 



The next problem was to investigate 

 the relation of insects to the trouble and 

 of course the first to be examined was 

 the aphis or green fly. These little pests 

 are present everywhere indoors and out- 

 doors and I do not ireed to tell you how 

 rapidly they breed and how difficult it 

 is to exterminate them, though they may 

 be kept pretty well under control by 

 constant attention. By colonizing these 

 insects on healthy plants it was soon 

 found that diseased spots were developed 

 wherever the insects punctured the young 

 leaves, but not in fully matured leaves. 

 The greatest care was taken to exclude 

 all bacteria; the surface of the leaves 

 was carefully sterilized with corrosive 

 sublimate and they were kept absolutely 

 free from bacteria. Still under these 

 conditions the disease was invariably pro- 

 duced whenever the aphides punctured 

 the young leaves. The spot did not be- 

 come apparent irr the leaf until several 



PItr. ."•• The gelatinous sheath left when the 

 phis withdraws its bill (dark lines extending 

 own into the leaf from S). In each case the 

 luncturc occurs just to one side of a breathing 

 lore. The Insect was evidently hunting for a 

 ascular bundle. 



The Carnation in Health and Disease. 



days after the puncture was made, some 

 plants reacting much more quickly than 

 others. Young growths reacted more 

 quickly than older growth, and in mature 

 leaves, as I have stated, there was no 

 apparent reaction at all. Aphides might 

 go on puncturing a plant for a week 



or so and then be killed by fumigation 

 or otherwise and for a time the plants 

 would appear to be healthy, though 

 later, perhaps after a week or ten days, 

 they would begin to show disease. It is 

 probable that the apparent infections with 

 bacteria that Dr. Arthur and Prof. Bol- 

 ley obtained were on plants which had 

 been previously punctured in this way 



Pig. ci. The enlarged cells In the piim'tured 

 area. The chlorophyll bodies have disappeared 

 and the light is thus permitted to pass through 

 the leaf readily making a transparent yellowish 

 spot in the tissues. 



The Carnation in Health ard Disease. 



but which at the time the inoculations 

 were made appeared to be perfectly 

 healthy. 



The question now arose why should 

 the punctures of the insect produce spots 

 which kept on increasing in size, finally 

 severely injuring the plant? In order to 

 get some light on this question aphides 

 were suddenly killed while they were 

 feeding on the leaf and sections very 

 carefully cut showing how they obtain 

 their nourishment and from what part 

 of the leaf structure it comes. The next 

 illustration (Fig. 4) shows one of these 

 sections. Tlte sucking apparatus of the 

 insect is thrust between the cells of the 

 very center of the leaf, there drawing 

 from the stores of food which the ear- 

 nation plant had made for its own use. 



The insects suck this food material 

 fiom the tissues and excrete the sugar 

 as honey dew, forming bright sticky 

 spots on the leaves. The result of course 

 is first of all partial starvation for the 

 whole plant, which becomes more or 

 less apparent by the stunting and some- 

 times the distortion of the plant, ac- 

 cording to the quantity of food removed 

 (Fig. 8). The trouble does not stop 

 here, however. 



When the insect sticks its bill into 

 the tissues it injects a urlat iiMu- >ub- 

 stan.e. which is left \.vU,.,;i t lie rolls 



eii.e of this material i> ...-ily detected 

 by the aid of a good microscope. The 

 iH'xl illtistiation (Fig. 5) shows some 

 of it >taincd between the cells in a very 

 voting diseased spnf. s. « ,, extending 

 as dark lines d..<Mi iiii<. ili. leaf. Grad- 

 ually the cells s upIiiiu this material 



become paler and ikiI.i m . nior and swell 

 up to several times tlicir normal size, 

 Fig. 6. The protoplasm breaks down 

 into minute granules resembling bac- 

 teria, and these on the death of the cell 

 run together into globular masses, re- 

 setnbling some kind of fungus, though 

 they are really nothing but dead proto- 

 plasm. 



Fig. G shows the enlargement of the 

 cells in the punctured area and the pro- 

 gressive development of the malady. The 



