552 Journal of Agricultural Research voi.xv.no.io 



a. . . -_ 



by insects, rodents, or birds; (4) the cutting off of the roots below ground 

 by insects in the soil which presumably feed on them, or by moles which 

 accidentally break them in working through the soil; and (5) the breaking 

 over of the stem, usually at the soil surface, as a result of repeated bend- 

 ing by wind or possibly by other agencies, sufficient to finally cause the 

 collapse of the cortex without transverse rupture of the epidermis or 

 vascular system. 



The first four types need little mention, as there is no danger of their 

 being confused with any of the other types of disease mentioned in this 

 article. A few observations on the factors influencing the washing out or 

 breakage of seedlings in artificial watering may be of interest. It devel- 

 ops that the fine spray from nozzles which some nurserymen use in 

 watering germinating seed beds will in some cases cause much more loss 

 through the washing out or breakage of seedlings than some other meth- 

 ods of watering. The best types of stationary sprinklers are less harmful. 

 Another much more drastic method of appl}dng water has also been 

 found relatively harmless. It appears that the washing out wliich com- 

 monly occurs is due not so much to the amount of water applied as to the 

 angle at which it strikes the bed. This at least seems to be the case in 

 the sandy soil vv^here most of the writers' watering experiments were con- 

 ducted. A fairly strong spray from the nozzle, by striking the surface of 

 the bed at an angle, as it practically always does, seems to displace soil 

 particles to a much greater extent than a very m.uch heavier mass of water 

 striking the surface of the bed directly from above. Ver)^ shallow-sown 

 seed beds have been watered without injury, by applying the water di- 

 rectly from the end of a i -inch hose line without nozzle or even coupling, 

 the end of the hose being so held that the water was spread out over the 

 hand of the man holding it and fell vertically on the beds in a rather thin 

 sheet. In this way water was applied to the beds wth good pressure 

 from large mains and hose leads at the rate of 15 gallons per minute, 

 while on the same beds a nozzle closed so as to give a spray and delivering 

 only from 3 to 5 gallons per minute caused considerable washing out. 



The fifth type of mechanical injury mentioned in the foregoing is one 

 which, though probably not uncommon, is very difficult to distinguish 

 from whitespot due to heat, and may also be confused with damping-o£f. 

 Plate B, figure 7, shows a seedling which was found broken over with 

 characteristic white-spot symptoms at a time following high wind and 

 cold, cloudy weather. The conditions were such as to seem to preclude 

 the possibility of heat as the cause, and the lesion differed from the ordi- 

 nary heat lesion in having the constriction more definitely limited to a 

 particular point, not involving the stem either above or below that point. 

 Much the same symptoms were later produced in a seedling of western 

 yellow pine by exposing it to a strong wind. Simple mechanical bending 

 was then tested on seedHngs of jack, red, and western yellow pine. As 

 expected from the experience in the seed beds, lesions such as those in 



