CR IT TOGA MO IS T )' I'ES. 



s:i 



The flat part of tlio Lichen is the tliallus, or vegetative por- 

 tion, while tlie yellow, cup-shaped disks (the apiAhiTia) 

 contain the fructification. Fitj. ."UT shows a section of 

 the apothecium, and also the lobing of the margin of the 

 thallus. Fi{?:. 3 IS is a \Qxy hi;;hly niafjnlfied view of a 

 section of a thallus, showing; it to bu lari^'cly made uj) of 

 cells, or /<//y>//aj, similar to those of the Mushroom. But 

 in f lie Lichen there are visible, in addition, large numbers *• 

 of spherical green cells {<j y in the figure) known as ijon- - 

 idia, which either occupy well-marked layers, as in the 

 present instance, or are scattered through the body of the 

 thallus. The presence of the gonidia may be said to be 

 the distinguishing feature of the Lichens. Their true 

 relation and function were for a long time doubtful, 

 widely difforent opinions being held, but it is now gener- 

 ally admitted that the gonidia are themselves ihlorophyll- 

 l»(trinif plants, and that tlie remainder of the Lichen is 

 a true Fungus, parasitic upon the yonidia. 



The structure of the apothecium is very well shown in Fig. 

 olO. From the hi'iihte are develoj^ed large, club-shaped, 

 vertical cells (the asri) which penetrate between the nar- 

 rower vertical branches of the hyphse (the para]>liysts). 

 In the asci arise the spores (technically ascasporcs), 

 usually eight in each, and these when mature are dis- 

 charged from the asci, and give rise to new plants. The 

 ascospores are formed in the asci by the process known 

 as /ri:e cell-fornudion. Tlie protoplasm in the asci col- 

 lects about as many different points as there are spores to 

 be formed, and a wall is then secreted about each. This 

 mode, which is characteristic of a large numljerof Fungi, 

 is (juite distinct from that which prevails in the Mush- 

 rooms, where, as we have seen, the s])Ores are formed bj' 

 iihstriction, 



Chara. 



Fig. 320 represents a Chara of the natural size. It grows 

 almost anj'where in fresh waters, and is quite readily 

 distinguished from other thread-like aquatics by the 

 whorls of so-called leaves which encircle the stem, ami 

 also bj- the general gritty-nature of the plant. A very 

 offensive odour is emitted by the plant in course of decay. 

 Its green colour shows at once the presence of chloro- 

 phyll. On the branches you may observe hundreds of 

 minute, more or less rounded, bodies ; Fig. 321 is an 

 enlarged view of one of them. Here, at fe, is shown a 

 large central nucleus (the fitwtde) enclosed in a spiral 

 covering. This spiral consists of five long cells side by 

 side, all of which wind about the central body, and have 





Flif. 31.1- 



Fljr. 51". 



