ERGOT. 147 



tions of the organs having been gradually decaying up to 

 that period ; when they have decayed completely the 

 part thence becoming dead or sphacelated, is thrown 

 off from the healthy portions. The separation of these 

 dead portions from the sound ones, is no more depen- 

 dent upon the division of the spiral vessels or such 

 individual circumstances, than separation of a gan- 

 grenous part from an animal body is upon a solution 

 of a continuity in the arteries or veins, but is brought 

 about by some general process affecting the whole struc- 

 tures at the line of demarcation between the two por- 

 tions, a local action having its origin in the whole vital 

 powers of the individual. 



9. Du Petit Thouars gave as a reason for the fall of 

 the leaf, a snapping of the spiral vessels, which keep up 

 the communication from th'e leaf to the interior of the 

 plant, brought about by the increase of distance taking 

 place between the leaf and the medullary sheath by the 

 deposition of new wood between them ; and Decandolle, 

 the hardening and choking up of the vascular and ex- 

 haling structures which ensue from the solid matters 

 left after the exhalation of their dissolving media. 



ERGOT. 



10. The disease of Ergot, or Spur, is seen attacking 

 certain kinds of Grasses, chiefly used for domestic pur- 

 poses ; and more especially Rye. 



11. Some have looked upon it as a disease of the 

 grain occurring spontaneously, others as the result of 

 injury by insects ; but it is now generally considered 

 that Decandolle has sufficiently proved it to be a distinct 

 parasitic plant, which locates itself in the ovary of the 

 grass. By the presence of the Acinula clavus in the 

 ovarium, the seed and its coverings, instead of being 

 properly developed, are perverted at an early period of 

 their growth, becoming partially mixed up with the 



