RECENT RESEARCHES INTO THE NATURE OF LICHENS. 155 



fig. 3, cannot fail to suggest that the increase in size exhibited by 

 the latter must be attributed to the influence of the Fungus. 

 They have ceased to undergo division, whereas the free gonidia 

 have given rise to numerous individuals. Other hyphse grow and 

 ramify, and although they come here and there into contact with 

 gonidia, they do not grow round them, but continue to grow in 

 a straight line along the surface of the slide. These hyphge cor- 

 respond to those which, on a normal substratum (rhizines) pene- 

 trate into it and act as absorbing organs. 



The cultures of Endocarpon made in this way, although the 

 plants continued to live for as long as six months, were never so 

 successful as to produce a thallus distinctly differentiated into 

 cortical and medullary portions; apparently the conditions were 

 altogether too abnormal. An endeavour was made to make the 

 conditions more favourable by substituting for the glass-slide, as 

 a substratum, a piece of porous earthenware, the cavities of which 

 had been filled up with soil deposited from suspension in water. 

 Under these circumstance the young thallus presents at an early 

 stage a dift'erentiation into an upper portion which contains the 

 gonidia, and a lower which is subterranean. (Figs. 4 and 5). 

 The structure of the upper portion is at first very simple, consist- 

 ing of a mass of closely-packed gonidia and hyphse invested by 

 a layer of pseudo-parenchyma, but gradually a difi"erentiation 

 into a cortical and a medullary part, with an intervening gonidial 

 layer, becomes apparent. The lower, subterranean portion 

 (hypothallus) consists of colourless, septate, branched and anas- 

 tomosing hyphse, some of which are isolated and others are 

 aggregated in bundles. 



Soon after this stage of development has been attained the 

 first Spermogonia make their appearance. They are ovoid in form 

 and are completely sunk in the thallus ; they contain no gonidia. 

 The first appeared within six weeks after the sowing of the spores, 

 and very shortly afterwards the first formation of perithecia be- 

 came evident. The first spores came to maturity within four or 

 five months. 



The history of the hymenial gonidia which did not become 

 invested by hyphse affords some interesting facts. It has already 

 been mentioned that they divide, and that the products of their 

 division do not exceed in size the mother-cells from which they are 

 derived. The divisions take place in one direction only, namely, 

 at right angles to the longer axis of the cells, so that the Alga 

 ought to be considered in this condition to belong to Naegeli's 

 genus Stichococcus, were it not that further observations shew 

 that these two genera must be united. 



Frank has suggested that possibly the gonidia, in consequence 

 of having been for many generations so intimately associated with 



