TREE ROOTS : THEIR ACTION AND DEVELOPMENT. 



13 



The Endotrophic mycelium of the larch never shows more 

 than a tendency to become irregular and swollen, and septa are 

 numerous and well defined. In certain cells the mycelium is 

 embedded in dotted areas (Fig. 6B) which may represent 

 products of disintegrated mycelium. No close association of 

 cell nucleus with digestion, however, if it be digestion, can be 

 demonstrated. 



Closely associated with the intracellular mycelium is a 

 strong growth of intercellular filaments. This mycelium 

 completely envelopes each cortical cell, separating each from 

 its neighbour. The intercellular hyphae penetrate the cell 

 walls of the cortex freely and easily, forming the endophytic 

 form, no constriction being formed at the point of penetration. 

 A noticeable feature of the Endotrophic form of the larch is 

 that the mycelium refuses to stain with cotton blue or gentian 

 violet, pointing to the cell contents having disappeared. This 

 only applies to mycelium in older roots. 



Very seldom do fungal strands appear to the outside of the 

 larch mycorhiza. The mycelium in the seedling first appears 

 between the cells of the cortex, and thereafter penetration of 

 the cell walls occurs. The first stage in the development of 

 the mycorhiza is really a semi-Ectotrophic form, and the 

 ultimate form is a semi-Ectotrophic form in association with an 

 Endotrophic form. 



Thuja Gigantea. 



This species has been found to produce only Endotrophic 

 mycorhiza. The mycorhiza are not beaded, i.e. there are 

 no constrictions separating off each successive growth 

 from the previous one, the roots simply growing in length 

 normally. 



Where the fungus is present no root-hairs are developed. 

 The whole root-system has a reddish hue, more particularly at 

 the root-tip, and is fresh in appearance, giving the impression 

 that a very great part of the system is absorptive as compared 

 with plants which are without mycorhiza. 



On cross-section the reddish colour above mentioned is found 

 most prominently in the region of the endoderm. The fungus 

 is widely distributed throughout the cortex (Fig. 7), appearing 

 within the cortical cells and also in the intercellular spaces. 

 Septa are of extremely rare occurrence on the mycelium, and 



