Histogenesis in Roots of Nothofagus solandri var. cliff ortioides 
(Hook, f.) Poole 
B. C Arnold 1 
An indigenous evergreen tree, Nothofagus 
solandri var. cliff ortioides, forms forests which 
dominate mountainous regions of New Zealand. 
The character of the root system varies ac- 
cording to the degree of mycorrhizal infection 
(Arnold, I960). Mycorrhizal roots are much 
branched and stunted by comparison with un- 
infected roots (Fig. 1). In cross-section mycor- 
rhizal roots are seen to be enveloped by a mantle 
of hyphae which penetrate in the form of a 
Hartig net between the radially elongated epi- 
dermal cells (Fig. 2). 
Maximum development of mycorrhizas is 
found where leaf-mold, moss, and humus are 
abundant on the forest floor, and the highest 
incidence of fleshy non-mycorrhizal roots is 
found in boggy soil, or when the tree is grown 
in cultivation in heavy garden loams. 
The present investigation was undertaken to 
determine whether or not the apical organiza- 
tion of Nothofagus mycorrhizas differed from 
that of uninfected roots, and to compare the 
histogenetic pattern of Nothofagus roots with 
that of the European beech Vagus sylvatica. 
I am indebted to the University Grants Com- 
mittee for a research grant in aid of this work. 
METHODS AND MATERIALS 
Uninfected roots and mycorrhizas were fixed 
at fortnightly intervals throughout the year in 
the following solutions: tannin fixative (Johan- 
sen, 1940); chromium sulphate fixative (Johan- 
sen, 1940); cytoplasmic fixative (Marengo, 
1952); formo-acetic alcohol (Johansen, 1940); 
Bouin’s fixative (Baker, 1950); acetic alcohol 
(Darlington and La Cour, 1947). 
Dehydration was carried out in a closely 
graded series of ethyl alcohol; clearing was done 
1 Department of Botany, University of Canterbury, 
Christchurch, New Zealand. Manuscript received July 
7 , 1964 . 
in alcohol-benzene mixtures; the specimens were 
embedded in paraffin; and serial sections were 
cut at 10 g. 
The following stains were employed: analin 
blue + safranin (Johansen, 1940); methyl violet 
+ erythrosin (Johansen, 1940); methyl violet + 
eosin (Johansen, 1940); Crystal violet, chromic 
method (Darlington and La Cour, 1947); Feul- 
gen technique for slides (Darlington and La 
Cour, 1947); Chlorazol black E + Aceto carmine 
(Nebel, 1940); Chlorazol black E (Cannon, 
1941); Iron-alum ammonium sulphide (Wig- 
glesworth, 1952). 
This wide range of fixatives and stains was 
employed in an attempt to determine whether 
the hypodermis of mycorrhizas contains living 
substance or whether it is in fact relatively 
empty of protoplasmic content. 
OBSERVATIONS 
In uninfected roots of Nothofagus solandri 
var. cliff ortioides the meristematic regions which 
give rise to epidermis, cortex, stele, and rootcap 
are readily distinguishable (Fig. 3) and their 
arrangement is similar to that reported for 
Fagus sylvatica (Clowes, 1961). While it is 
convenient to refer to these tracts of meri- 
stematic cells as dermatogen, periblem, plerome, 
and calyptrogen, respectively, I have been unable 
to conclude whether or not they represent en- 
tirely discrete histogens in the original sense of 
the word. 
Despite the very considerable histological 
modification of root structures in mycorrhizas, 
including a reduction in the size of the pro- 
meristem, it is possible to identify in them a 
dermatogen, periblem, plerome, and vestigial 
calyptrogen in much the same relationship as in 
uninfected roots. The maturation of derivatives 
of the promeristem of mycorrhizas is greatly 
accelerated, and the derived cells are often re- 
duced in number. 
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