486 



AMERICAN FORESTRY 



STRANGE DISEASE of PLANTS 



Fig. 3 Another view of the manner in which hypertrophy at- 

 tacks a tick trefoil showing the seeds distinctly. Note hon cur- 

 iously the stem is enlarged. 



parts coming into existence, but that galls, with every- 

 thing that was to be found in them, were produced in a 

 similar way, that is, through the agency of the "vegetable 

 soul." The fact will be appreciated that these early stu- 

 dents and observers had never noticed the female insect 

 deposit her eggs in such places on plants and trees as 

 where the galls subsequently appeared ; so it was con- 

 tended by many that she deposited her eggs in the ground 

 about the roots of trees and plants, and that, later on, the 

 eggs thus lain were carried by the sap of the plant or 

 tree up into the leaves, twigs and small limbs ; passing 

 along as far as they could, they finally lodged, and galls 

 formed in those places as a consequence. 



Along in 1760 a closer observer and more intelligent 

 writer appeared in the field. I refer to the Italian natur- 

 alist, Filippo Arena, who had given to the world some 

 useful facts on the cross-pollination by insects in the 

 case of plants; but he carried the discovery too far when 

 he claimed that trees and plants produced galls, in that 

 the insects that came from them might be sufficiently 

 numerous so that cross-pollination should not fail during 

 any particular year for the lack of a supply of those 

 insects responsible for it. 



Finally the true cause of a plant gall was announced, 

 and this by the Italian anatomist and microscopist. Mar- 

 cello Malpighi, who, towards the close of the 17th cen- 

 tury, pointed out that galls on plants and trees were 

 caused through the punctures made by certain insects; 

 and that as swellings they were due to those punctures, 

 just as swellings on our own bodies result from the sting 

 of bees or other insects capable of inflicting a venomous 

 wound. Here the matter now stands, little having been 

 added to Malpighi's theory during recent years, although 

 the subject has been investigated and extensively con- 

 tributed to by not a few able writers. At this writing, 

 hundreds upon hundreds of plant galls are known, and 

 have been more or less fully described by the various 

 investigators of the subject. They are now known to 

 occur on plant growths of every description, even many 

 fungi coming in for a share of them. Few are aware 

 of the fact that potatoes are merely fungus galls on the 

 roots of that plant ; and others of them on our legumi- 

 nous plants are chiefly responsible in producing the 

 nitrogen of the air, in that it may be utilized by 

 growing plants. 



A LEAF-CROWNED STEM OF A GOLDENROD 



Fig. 4 Not only does goldenrod exhibit the, curious condition 

 here shown, but it likewise often presents elongate galls on 

 the stem of the plant, as illustrated in another figure. 



