ELISHA MITCHELL SCIENTIFIC SOCIETY. 129 



EXPLANATION OF PLATES. 



[All the Plates are original, and except the first two, which are from photo- 

 graphs, were drawu by the author from nature. In Plates IV, V and VI all the 

 figures are magnified except 31 and 32. J 



PLATE I. Irish Potatoes {Solarium tuberosum). — The cracks in the large 

 potato (seed potato) result from the increased growth of cells at the points where 

 the Heterodera exists. The upper left-hand figure is a small 5'oung potato taken 

 from this same plant, the elevations and projections caused by presence of the 

 Heterodera. The enlargements on the roots of the potato are the galls. (Natural 

 size, from photograph). 



PLATE II. Tomato root showing root-galls two-thirds (natural size, from pho- 

 tograph). 



PLATE III. Parsnip and Salsify, showing root-galls, natural size. 



PLATE IV. Development and transformation of Heterodera radicicola (Greef). 

 Miill. 



Figs. 1 — 9, different stages in segmentation of mature eggs ; 10, invagination 

 at anterior pole; 11, young embryo of the length of the egg, beginning to elon- 

 gate and coil inside of the egg membrane, the caudal end, which is below in the 

 figure turning toward the ventral side, the cephalic end, above, granular and 

 nearly hyaline ; 12, 13, 14, farther elongation of embryo ; 15, mature larva coiled 

 five times within the egg membrane. 



Fig. 16. Larva coming from egg membrane and moulting at same time, the 

 partially cast skin can be seen slipped from the head and tail. At the boundary 

 between the hyaline and strongly granular portion near the tail end can be seen 

 the anal opening. 



Fig. 17. Sexually immature worm, larva: 17x, same, not so greatly magnified 

 in one of the various forms sometimes found prior to the cystic state ; 18, 19, 19^, 

 various degrees of distention of the larva ; 20, young female cyst, showing 

 ovaries ; 21, male undergoing metamorphosis ; 21a; and 22, same with metamor- 

 phosis complete, in pupa state ; 23, emergence of sexually mature male from 

 cyst ; 24, front view of head of male showing the position of the lamellne around 

 the spear ; 25, anterior end of female, a exsertile spear, h anterior part of the 

 oesophagus ; 26, posterior end of a male (see page 103), a caudal appendage 

 (probably an accidental variation), h spicules; 21^ sexually mature male very 

 greatly magnified, showing the paired testes. 



Fig. 27. Mature female cyst, a middle part of oesophagus (suctorial bulb), h 

 anterior part of oesophagus, c exsertile spear, d vulva, e genital tubes, the anterior 

 ends of which form the ovaries. 



Fig. 2vS. Genital tubes of female cyst with mature eggs still farther enlarged ; 

 a vagina ; the uterus extends from the vagina a little more than one-third the 

 length of the tube, near the middle is the recepiaculwn seminis, the oviducts and 

 ovaries occupj' a little more than one-half of the free ends. The small ova are 

 very tender and flexible, but by pressure of the mass are held in a polygonal form 

 within the ovaries. If the ovary is broken at a point as at b or c the young ova 

 escape and assume a spherical form, and not yet being free cells are held together 

 in a beautiful cluster as represented in the figures. As the young ova increase 

 in size by growth the pressure causes them to move toward the oviducts, they 



