478 AMEIilCAX TEAR BLIGHT. 



comes firm. After a young cell has been formed, 

 the interior of its membraneous walls is constantly 

 receiving an increased coating of woody fibre. This 

 takes place most rapidly in the cool weather of the 

 autumn, after the growth has stopped, and the whole 

 force of the sluggish circulation seems to be directed 

 to this deposition. Consequently, it is then that 

 the young wood requires the greatest abundance of 

 carbon; and therefore an all-wise Providence sup- 

 plies strong winds and gales to ripen their sub- 

 stance. 



If a frost sufficient to destroy vegetation occurs 

 when the soft growth has just put forth, as in June, 

 1861, in some sections of the United States, all the 

 young parts of the- tree present the same stained 

 appearance as after blight. This results from the 

 cells' lesion, which precipitates the sap into the in- 

 tercellular spaces. This causes the burst cells to 

 decay, with all the other parts, which have been 

 corroded by the fusion of sap. As vegetable, like 

 animal tissue, is extremely sensitive to decaying 

 matter, not only these may be destroyed, but also 

 the decay may spread through the young parts of 

 the whole plant. 



The pear blight frequently occurs about the time 

 of thunder showers. According to experiments 

 made under the direction of the London Horticul- 

 tural Society, it was found that just before, during, 

 and immediately after a thunder-storm, the growth 



