KINDS OF MYCORRH1ZAE 301 



failure to distinguish between "long roots" and "short roots," as 

 pointed out by Hatch and Doak (1933). Frank (1885) and most 

 European investigators, including Alelin (1925), are in accord 

 that "short roots" are invariably mycorrhizal roots. Observations 

 by Noelle (1910) on the anatomical differences between long 

 roots (Bereicherungswurzel) and short roots (Ernahrungswurzel) 

 of pine, confirmed by Hatch and Doak (1933), are summarized 

 as follows: 



Long Roots Short Roots 



Root cap present. Root cap absent. 



Diarch or polyarch. Monarch. 



Have secondary growth. Lack secondary growth. 



Root hairs arise from second or Root hairs arise from epidermal cells. 



third layer of cortical cells. Branch dichotomously. 



Branch racemosely. Ratio of stele diameter to total di- 



Ratio of stele diameter to total di- ameter low. 



ameter high. 



These anatomical differences support the theory that mycor- 

 rhizae are distinct morphological structures, as Frank (1885) first 

 maintained. They also indicate that long roots are permanent 

 structures, whereas short ones are ephemeral, lasting at most 

 throughout one season. 



Hatch and Doak (1933), like earlier workers, distinguish three 

 kinds of short roots: (1) uninfected short roots, (2) pseudo- 

 mycorrhizal roots, and ( 3 ) mycorrhizal roots. 



The first kind is exceedingly rare and is characterized by the 

 following features: (a) formation of root hairs from epidermal 

 cells, (b) continuous slow elongation, (c) no hypertrophy of 

 cortical cells, (d) complete lack of fungal hyphae, and (e) dichot- 

 omous branching. 



The second type, called pseudomycorrhizae by Alelin, may be 

 differentiated by these characteristics: (a) absence of root hairs, 

 (b) early cessation of elongation, (c) complete absence of hyper- 

 trophy of root cortex, (d) lack of intercellular fungal net, (<?) 

 occasional dichotomous branching, and (f) intracellular invasion 

 by soil-inhabiting fungi. 



Endotrophic mycorrhizae, such as occur among Ericaceae and 

 Orchidaceae, are not to be confounded with the intracellular 

 hyphae in pseudomycorrhizal roots. These hyphae do not occur 

 in masses but may penetrate the cells in small numbers, involving 



