Kelley 



— 82 — 



Mycotrophy 



tention to the fact that some trees, as Tilia europaea, have greatest de- 

 velopment of roots in fall while in oaks the greatest development is in 

 spring. Other observations indicate similar generic differences : Thus, 

 Prat (1926) found that in Taxiis the long-roots grow throughout 

 the whole season with varying rapidity although cold lessens activity 

 and causes modification of the apex. Most of the absorbing rootlets 

 cease growth completely in winter, at which time the cortex dies from 

 the apex and exposes a red surface, while growth recommences in 





Fig. 4. — Renewed growth of mycorrhiza- 

 bearing mother-root of Piniis Strohus, new 

 white mycorrhizae being formed amongst 

 old dark ones, with some rhizomorphic in- 

 vesting mycelium also indicated. Collected 

 at Baltimore, 26 February 1930. 



spring. In pine, Rayner ( 1934) says positively that the mycorrhizae 

 are annual and only in exceptional cases is growth renewed. P. Bank- 

 siana is completely dormant in winter in Minnesota, the roots growing 

 from April to October (Kauffman, 1945). Again, McArdle (1932) 

 stated that mycorrhizae of spruce and pine are formed mostly in 

 September to November inclusive and that they are usually dead by 

 spring. Yet Preston (1943) found that pine mycorrhizae did not 

 appear to be "strictly annual", and several instances were noted where 



