168 ROBERT PAULSON ON THE 



alone, and for this purpose all the help that microscopical 

 technique can afford is required. The objects to be observed are 

 minute — a sphere with a diameter of from 10 to 12 /a, and a 

 thread 3 to 4 /* thick. Such objects give images that vary con- 

 siderably according to the method of illumination and the focusing, 

 but the solution is not beyond the reach of careful manipulation. 

 From the investigation it is inferred that there is no doubt 

 whatever that actual penetration of the living cell very rarely 

 occurs where the alga is Chlorella (Cystococcus of most authors) ; 

 the case of lichens with blue-green algae, Cyanophyceae, have not 

 yet been fully considered ; nor have those where the alga is 

 Trentepolia, which is of an orange colour. 



It has been generally assumed that the gonidia of lichens, 

 described above, increase in number by vegetative cell division, 

 and that spore formation takes place only when the gonidia 

 have been isolated from the thallus and subjected to cultural 

 methods. This assumption has probably arisen from the fact 

 that in one of the most important textbooks on Fungi, a book 

 used throughout the world, the following statement is found: 

 " In one point the Fungus is the superior in the common 

 household ; it alone produces spores, the alga with few exceptions 

 remains barren as long as it is combined with the Fungus." The 

 only exception given in this case is that of Synalissa symphorea, 

 a lichen with a blue-green alga. It is now possible to show 

 definite stages in the formation of spores within algal cells while 

 they are components of the lichen thallus. The original proto- 

 plast of the cell divides into 4, 8, 16 or 32 masses. The most 

 common numbers that have been found are 8 and 16. These 

 masses soon develop a cell wall, and within a short period they 

 resemble in all respects but size the mother cell, which rapidly 

 becomes diffluent, and thus the daughter gonidia escape (PI. 4, 



fig. 1). 



A great deal of what has been said is not in agreement with 

 the opinions of authors, but the claim is made upon the evidence 

 of preparations and an interpretation thereof as it presents itself 

 after a considerable amount of time devoted to the subject. 



There is an important factor to bear in mind in that the majority 

 of lichenologists have devoted their energies to the classification 



