Se es SS 
I.—PHYSIOLOGY. 203 
(1) When the potato plant and Orobus are raised from seed, the 
establishment of symbiosis leads to tuberisation of the sprouts at the 
base of the stem; tubers are not formed in the absence of symbionts. 
(2) Owing to developmental differences between the two plants, 
symbiosis in the potato plant is intermittent, whilst in Orobus it is 
continuous. (3) It follows that these plants may develop in two ways: 
(a) when they harbour symbionts they produce perennial organs; 
(b) without symbionts they are devoid of perennial organs. (4) It is the 
rule for wild perennials to hatbour symbionts, as Bernard has stated, 
whilst annuals are devoid of symbionts; three species of annuals 
(Solanum nigrum, Orobus cecineus, and Mercurialis annua) may be 
penetrated by endophytes, but they quickly digest the intruders. 
(5) These observations confirm and supplement the view held by Bernard 
that tuberisation is due to the association of fungi with plants. 
Mycorhiza in Ericacee. 
Rayner (1915-16) finds that Mycorhiza are constantly present in 
heathers. He isolated Mycorhiza (of the genus Phoma) from Calluna 
vulgaris, in which the fungus is widely distributed, being found in the 
roots, branches, and even in the carpels, so that it occurs within the 
ripe fruit and seed tegument. Calluna seeds, when grown aseptically, 
give rise to poor little plants devoid of roots, but, under like conditions, 
in contact with Phoma the plants develop normally and form many 
rocts. 
Mycorhiza in Club-mosses and Ferns. 
Tn Lycopodiacew (Club-mosses) and Ophioglossacee (Ferns), accord- 
ing to Bernard, the perennial prothallus is infested, and the spores 
whence the plants emanate will not germinate except (as with orchid 
seeds) with the help of fungi. 
In concluding this part of my subject, dealing with symbionts of 
plants, I need scarcely emphasise the significance of symbiosis in the 
vegetable kingdom, I will close by mentioning the theoretical deduction 
of Bernard that vascular plants owe their origin in the past to the 
adaptation of certain mosses to symbiotic life with fungi. 
II. Symbiosis in Animals. 
(1) Alg@ as Symbionts. 
Animals of widely separated groups characterised by their green 
colour have long been known. Already in 1849, von Siebold attributed 
the colour of Hydra viridis to chlorophyll which, for a period, was 
regarded as an animal product. In 1876, Gésa Entz concluded that 
_ the chlorophyll is contained in vegetable cells living as parasites or 
commensals within the animals; these cells were aptly named 
zoochlorella by Brandt (1881), whilst cells distinguished by their yellow 
colour were subsequently called zooxanthella, the latter having been 
first described by Cienkovsky (1871) as present in Radiolaria. In the 
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