INTRODUCTION TO CRYPTOGAMIC BOTANY. 213 



perhaps, be entertained were there no proper fruit ; but when 

 this is frequently of two kinds, and totally different from that 

 of the matrix, and there are, moreover, many closely allied 

 Algae which are not parasites, the belief is as absurd as that 

 of the supposed identity between the myriads of truly parasitic 

 fungi, and the plants on which they grow. Myrionema 

 presents a genus still less organised than JElacMstea, and by 

 reason of the difference of colour between the brown threads 

 and the red or green matrix the distinction is more evident. 

 These parasites all belong to the north hemisphere. Elachistea 

 extends as far south as the Canaries. Ralfsia forms a liche- 

 noid crust on pebbles, resembling in colour the more tawny 

 Zonarios. The fruit is of rare occurrence, and approaches 

 closely in character to that of Elachistea, growing, in fact, in 

 tufts much after the fashion of that genus. Leathesia occurs 

 in every part of our coast, attached to corallines, shells, rocks, 

 &c., either forming gelatinous pulvinate crusts, or tuberlike 

 more or less inflated masses. Different as this genus is in ex- 

 ternal habit, it is almost identical, in point of structure, with 

 Mesoglcea, which with Liebmannia forms filiform branched 

 slippery masses, composed of central articulated threads beset 

 with myriads of branchlets, consisting in great part of monili- 

 form filaments. Most of the described species belong to the 

 Atlantic; but Port Natal and the Philippines have their 

 representatives. The Philippine plant, at least, which I have 

 examined, is quite certain. Chordaria is merely a compact form 

 of Mesoglcea, but still of a strikingly gelatinous consistence. 

 In several of these plants the joints of the external threads 

 increase in diameter as they approach the surface, and are less 

 subject to the pressure of contiguous threads, and in such cases 

 the endochrome is generally more highly coloured and more 

 copious (Fig. 54) ; but such appearances are not to be mistaken 

 for fruit, which is often very distinct, and sometimes of two 

 forms, where the external cells are much developed, as in 

 Liebmannia. In no plant is this more marked than in 

 Chordaria divaricata, the terminal joints alone being 

 globose. 



