Nov. is, 1920 Hypertrophied Lenticels on the Roots of Conifers 257 



number of conspicuous, glistening, mound-shaped excrescences, as is 

 shown, slightly magnified, in Plate 46, C. A microscopic examination 

 of sectional preparations of these excrescences (Pi. 46, A) showed clearly 

 their lenticellular structure. The outgrowths were so loose and delicate 

 that the outer portions were necessarily lost in sectioning, but the figure 

 shows enough of the bases to indicate the type of structure. 



In general, root-lenticel hypertrophy has been found especially frequent 

 not only on species like western yellow pine, which are somewhat inclined 

 to lack fine fiberous roots, but also on individuals of other species when 

 a strong tap root has been developed with relatively little development 

 of laterals. Whether or not the larger lenticels are of advantage to such 

 plants in fulfilling part of the functions that the missing laterals might 

 have performed is of course uncertain. In this connection it is of some 

 interest to note the finding of root-lenticel hypertrophy in Michigan on 

 white and Colorado blue spruce (Picea canadensis and P. pungens) 

 whose roots had been injured by May beetle larvae. It is also especially 

 interesting that nursery trees that have not been transplanted or that 

 are in their second season in the transplant beds show decidedly less 

 hypertrophy than recently transplanted stock. The recently trans- 

 planted trees have, of course, lost most of their absorbing roots, while 

 the trees transplanted the preceding season have had a chance to develop 

 normal root system again after transplanting. 



IRRIGATION EXPERIMENTS 



Trees of Pinus ponderosa in their third year in the nursery, and two 

 months following transplanting, were given river water from the irri- 

 gating ditch frequently during a three months' period, beginning July 1 1 , 

 1 91 7. All the tests considered in this and the following section were 

 conducted at the Bessey Nursery in cooperation with Forest Supervisor 

 Jay Higgins and his assistants. The water added at each irrigation was 

 approximately equivalent to 2.2 inches (5.6 cm.) of rainfall. A bed 

 which received 31 such irrigations during these three months showed at 

 the end of the period 31 per cent of the trees with 8 or more distinctly 

 hypertrophied lenticels each and a total of 57 per cent with some evi- 

 dence of hypertrophy. The figures are based on an examination of 255 

 trees. This amount of watering was sufficient to cause more or less 

 chlorosis, especially of the shoots which arose after the watering began. 

 Another bed in the same section, on which the frequent watering was 

 not started until a month later and which received during the entire 

 three months a total of 17 irrigations, showed at the end of the period 

 eight or more enlarged lenticels each on approximately 13 per cent of 

 the plants examined. Other beds used as controls received the usual 

 amount of water given at this nursery, involving six irrigations in addi- 

 tion to the j.j inches (20 cm.) rainfall during the period of three months. 

 9508°— 20 2 



