November 17/1916] 



SCIENCE 



709 



from a large plate with deep radial flutings 

 and the other, smaller, with similar markings. 

 Both are evidently Stegocephalian. 



7. A large vertebral centrum, evidently 

 from a sterospondylus Stegocephalian. 



Most of the bones were found in the con- 

 glomerate beds, but a few in lenses of impure 

 limestone. 



Lee and Girty also give a description of the 

 beds near the Mesa del Yeso on the eastern 

 side of the Valle del Ojo de la Parida and re- 

 port typical Manzano fossils from the Teso 

 formation. 



The Red Beds were examined by the writer 

 near the Ojo de la Parida about ten miles 

 northeast of Socorro, where the Abo, Yeso and 

 San Andreas formations are easily recognized. 

 In the Yeso and the upper part of the Abo no 

 vertebrate fossils were found, but in the lower 

 part of the beds near the mouth of the Canyon- 

 cito Colorado (see the Socorro topographic 

 sheet) beds of dark red pebble conglomerate 

 were found lying upon 1 green, blue and drab 

 shales which show in the bed of the arroyo. 

 In this conglomerate were found typical 

 Permo-Carboniferous bones such as were col- 

 lected by Dr. Williston and the writer in Rio 

 Arribo County, New Mexico. The following 

 list shows the similarity: 



1. A complete femur of Eryops sp. 



2. The distal end of a clavicle of Eryops sp. 



3. The distal end of a neural spine of 

 Eryops sp. 



4. A femur of Sphenacodon. 



5. A fragment of the jaw with four teeth of 

 Sphenacodon. 



6. The distal end of the scapula of a Sphena- 

 codon or Ophiacodon. 



7. The distal end of a large scapula, pos- 

 sibly Sphenacodon. 



8. Fragments of a large pelvis, possibly 

 Sphenacodon. 



9. In the bluish shale in the bank of arroyo, 

 the proximal end of a rib of diadectid type 

 associated with poorly preserved plant remains. 



10. In the drab shale below the blue, several 

 invertebrates. 



The discovery of this fauna below the San 

 Andreas limestone adds one more bit of evi- 



dence to those already cited by the author 

 elsewhere, for the very early appearance of 

 specialized reptilian life in North America. 

 E. C. Case 



THE SWEET POTATO "SOIL ROT" OR "POX" 

 ORGANISM 1 



Since Halstead in 1891 published his results 

 on the study of " Soil Rot " of sweet potatoes, 

 which he credited to a fungus " Acrocystis 

 batatas," little positive work seems to have 

 been done on the causative organism. During 

 the present season observations by the author 

 of slimy masses on the surface of roots devel- 

 oping large shallow " pox " marks, led to the 

 discovery that the disease is due to a Plas- 

 modium and that there are two modes of in- 

 fection. One is by the Plasmodium as a whole, 

 causing large shallow pits; the second is by 

 means of swarm spores, which enter the grow- 

 ing-points of stems or roots and cause the 

 formation of deep circular pits, when the in- 

 fection reaches the main root. The swarm 

 spores first entering a growing-point go 

 through a rapid development in the outer host 

 cells, passing through an ameboid and a plas- 

 modial stage. During the plasmodial stage a 

 large number of nuclei are formed by mitotic 

 division. The Plasmodium then forms a 

 heavy-walled cyst in which hundreds of spores 

 are developed. The swarm spores are liber- 

 ated within the cyst, which breaks down and 

 releases the spores, when a further infection 

 of host cells occurs. The infection spreads 

 rapidly to the main root, causing a pit or 

 " pox " scar. When the pit has reached the 

 limit of its development the Plasmodium as- 

 sembles and breaks out, migrating into the 

 soil. A secondary infection by swarm spores 

 in small immature pits, causing extensive 

 blister-like elevations in the skin of stored 

 sweet potatoes, has been observed. White 

 potatoes are also subject to the disease. 



The formation of a heavy-walled cyst con- 

 taining several hundred swarm spores sepa- 

 rates this Plasmodium from the now-recog- 

 nized genera of the Plasmodiophorales. Ac- 

 cordingly, the name Gystospora batata gen. 



i A preliminary note. 



