Lancaster. — The Fungi of New Zeahnid E jii phjitic Orrhu/s. 191 



sufficient. The nitrogen compounds of humus arc in general far too complex 

 for ordinary green plants to assimilate. In view of this fact the idea that 

 the fungus of the mycorhiza in some way assists in increasing the nitrogen- 

 supply does not seem unreasonable, and the experimental work of British 

 and Continental investigators tends to show that there are good grounds 

 for this supposition, at least in the case of the particular plants investigated 

 by them. 



With regard to the New Zealand epiphytic orchids, it is impossible in 

 the absence of experimental investigation to make any positive statements 

 as to the uses of the mycorhiza. In view of the evidence in hand, how- 

 ever, the following may be held to represent in a general way what occurs, 

 and to be a brief statement of the working hypothesis : — 



Fungal hyphae living in the humus in which the orchid-roots are usually 

 imbedded penetrate the spongy velamen tissue and wander about in its 

 cells, and probably derive some slight advantages therefrom. It has been 

 remarked above that this tissue is sometimes found to be in a state of decay. 

 That the hyphae may have something to do with this is not impossible. In 

 this dead velamen tissue they meet with no active resistance. Finding 

 points of weakness in the exodermal cylinder — e.g., the transfusion-cells — 

 they enter. Here, however, they are for the first time face to face with 

 vigorous living cells, and after forming a scanty coil they branch out into 

 the cortex. The orchid now becomes the aggressor, and its protoplasm 

 absorbs what it can from the hyphae, producing in them the vacuolated 

 appearance previously mentioned. After forming several coils in the 

 cortical cells the hyphae are exhausted, and the protoplasm of the orchid 

 still continuing to absorb, eventually kills them. It soon changes a dense 

 coil of filaments into a yellowish unorganized mass, which probably repre- 

 sents the parts of the fungus which the protoplasm is slow to assimilate, 

 or which it is unable to assimilate. The nuclei of the cortical cells show 

 the result of the vigorous nutrition in their greatly increased size. The 

 three types of masses above described represent the coils of hyphae in 

 dii?erent stages of absorption. The observation of a very large number 

 of sections of the roots shows that something like this is actually what 

 occurs. The appearance of a mycorhiza is held by some to indicate incipient 

 saprophytism. If this view is correct, the New Zealand epiphytic orchids 

 may be just beginning a career as saprophytes. 



The position of the fungi of these mycorhizae in the classificatory scheme 

 has not yet been determined. Culture experiments have been made, but 

 I do not regard their results as absolutely convincing. I am hopeful, how- 

 ever, that a few more experiments of this kind will enable the systematic 

 positions of the fungi to be accurately determined. It is worthy of note 

 that spores are often observable in the velamen tissue, especially in the older 

 portions of the roots, and most commonly when the roots are freely exposed 

 to the air. In several cases the whole of the hyphae in the velamen had 

 broken up into chains of spores. 



