124 Rayner.—Obligate Symbiosis in Calluna vulgaris. 
for systematic reasons, and favours the view that the members of this sub- 
order are closely related to the hypogynous forms. 
Since ovarial infection is the rule, the seeds of all species will evidently 
always be liable to infection by the specific Fungus; whether the relation 
between seedling and Fungus is of the same obligate character as has been 
demonstrated for Calluna can only be determined by experimental investi¬ 
gation of each case. The observation recorded by an earlier investigator, 
that young seedlings of Andromeda polifolia germinating viviparously in 
the capsule showed fungal infection of the roots, is worthy of notice in 
this connexion ( 26 ). 
Experimental investigation is also required in order to determine 
whether the endophyte is specific to each plant species, or can be used 
successfully for the inoculation of any member of the group in which an 
obligate relation can be demonstrated. 
Appended is a list of the species in which ovarial infection has been 
observed, and a similar distribution of the Fungus may probably be 
inferred. 
Rhododendroideae. 
Ledum palustre , Rhododendron ponticum (Garden var.), Rhododendron 
indicum (.Azalea indica , garden var.), Rhododendron sinense (.Azalea sinense , 
garden var.), Leiophyllum buxifolium , Kalmia angustifolia . 
Arbutoideae. 
Pier is jloribunda, Pier is japonica , Gaultheria acutifolia , Arctostaphylos 
Uva-tirsi , Arbutus One do. 
Vaccinioideae. 
Vaccinium Vitis-idaea , Pentaptergyium serpens. 
Ericoideae. 
Calluna vulgaris , Erica carnea. 
Summary. 
i. In common with other members of Ericaceae, Callitna vulgaris 
possesses a characteristic root mycorrhiza. 
1 . Infection by the mycorrhizal Fungus takes place shortly after 
germination, the source of such infection being the testa of the seed. 
3- Infection does not cease with the formation of the characteristic 
mycorrhiza associated with the roots but affects all parts of the young 
seedling. 
4. In the mature plant, likewise, the Fungus is not confined to the roots 
or colourless parts, but is present also in the sub-aerial organs—in the tissues 
of the stem, leaf, flower, and fruit. 
