544 SUMMARY or CURRENT RESEARCHES RELATING TO 



When the nutrient fluid is more concentrated or contaminated 

 with bacteria, multiplication is greatly hindered; the myxamcebse are 

 larger and put out lateral pseudopodia ; the proportion of hyaloplasm 

 is smaller, and the movements slower, finally ceasing, the vacuole 

 ceasing at the same time to pulsate. The myxamceba is then 

 spherical, 12 to 15 fj. in diameter, with a yellow or brown membrane, 

 and may be termed a microcyst. The application of reagents shows 

 the membrane to be double. The microcysts may remain at least a 

 month, and even dry up without losiug their power of germination. 



The whole process of development lesembles closely that of 

 Guttulina rosea Cienk. ; but the present species is distiuguished by its 

 size and absence of colour. 



Lichenes. 



Structure, Development, and Life-history of a Tropical Epi- 

 phyllous Lichen.* — H. M. Ward's observations led him to believe 

 that the epiphyllous cryptogam examined by him supports the 

 Schwendeneriau theory that a lichen is a compound organism com- 

 posed of an alga to which an ascomycetous fungus has become more 

 or less intimately affixed. It is developed on the leaves of many 

 plants, but it has been more closely watched on Michelia furcata. 

 The lichen presents four types — orange-red, stellate patches, gi-eyish- 

 green blotches, clear grey spots, and white shining circles ; but these 

 pass imperceptibly into one another, and vary in size from a speck to 

 l-4th in. in diameter. The reddish spots of the earlier stages are 

 alg£e, of which the radiating filaments are in i)art reproductive organs, 

 and in part barren hairs. The alga subsequently passes into the grey 

 and green stages, and by a modification of growth the invasion of a 

 fungus-mycelium succeeds. The white matrix of the complete lichen 

 consists of the same algal thallus invested by dense masses of the 

 fungus hyphae, which produce shining black dots, viz, the fructi- 

 fication. 



The author describes in detail the peculiarities of growth and 

 reproduction of the alga and fungus, and the formation of the lichen. 

 He alludes to and criticizes Dr. Cunningham's account of Mycoidea 

 parasitica, which plant is evidently closely related to that described 

 by himself. Assuming that Mycoidea and Ward's alga are generically 

 the same, either Cunningham discovered a female organ of reproduc- 

 tion which becomes fertilized and produces zoospores, or he confounded 

 this with " fertile hairs." 



As regards the systematic position of the alga, a comparison with 

 Coleochcete suggests that there is very little in common beyond the 

 mode of growth of the disk-like thallus and the production of zoo- 

 spores from certain cells. The genus Chroolejms, moreover, presents 

 features which agree in several important points, viz. orange-red oily 

 cell-contents, habitat, and production of zoospores in ovoid cells, de- 

 veloped terminally and laterally. The structure of the thallus, and 

 the relative positions of the main masses of fungal and algal portions 



* Trans. Linn. Soc. Lond. (Bot.) ii., 1883, pp. 87-119 (4 pis.). 



