THE LTCIIEX SYMT^IOSTS 2G3 



ization may be expressed in terms of: (1) dorsiventrality; of (2) uni- 

 facial type ; (3) lobing or proliferation ; (4) ramiHcation, appearing 

 more or less dichotomous ; (5) continued growth at the end; (G) a 

 certain amount of intercalary extension, responsible for the broad area 

 so readily attained ; (7) marginal apothecia, otherwise of normal 

 Discomycete categorj^ The general organization is that of a mere 

 blanket-tyj^e of hyplial weft, formed of felted septate hyphse, 10-12 jx 

 diam. Beyond the normal production of ascospores in apothecia on 

 marginal lobes or ramuli, three or four undoubted form-factors may 

 be isolated, without straining, as calling for comment or explanation 

 as to the causes which may have produced them as part of an 

 elaborate phj^siological mechanism. 



II. From such a type Physcia parietina, the common yellow 

 crustaceous lichen of slate-roofs, M^th included Cystococcus, differs 

 only in adding dorsiventral bifacial construction, as the peripheral 

 pseudoparenchymatous weft is differentiated on the lower surface 

 of the thallus as 'well, inhibiting the extensive rhizine-system of 

 Peltigera, and suggesting a further xerophytic adaptation and control 

 in terms of a far more substantial pseudoparenchymatous screen. 

 Otherwise there is no special ramification beyond a mere peripheral 

 lobing of the thallus-margins. That is to say, taking such types of 

 dorsiventral and crustaceous lichen only, there seems much to be said 

 for the new somata being much alike, since with different Fungi and 

 different Alga3, the form-factors present much in common. 



III. But in the case of Usnea harhata one finds a thallus of 

 quite a different type, presenting factors of (1) centric, or radial 

 organization; (2) copious ramification; (3) any lateral may extend 

 as a leader, without rule, or ]*emain a short filamentous process ; 

 (4) the ramuli show apical growth and differentiation ; (5) inter- 

 calary extension is restricted ; (6) the internal differentiation of an 

 axial strand of hypha?, mainly parallel in direction, of skeletal value, 

 may be distinguished from (7) the loose weft of the cortex, with 

 again a dense and continuous peripheral tract of pseudo-parenchyma ; 

 (8) broad apothecia with normal details terminating special ramuli 

 as in Peltifjera ; the whole organization a well-marked branching 

 ' fruticose ' type, attached by a definite hapteron of hyphal fila- 

 ments, as a bushy type of growth which may attain a length of a foot 

 or more in associated species, presenting so close a copy of an auto- 

 trophic plant-form that one forgets to remejuber that it is merely a 

 product of a dual ' synthesis.' 



IV. Cladonia sylvatica, again, as a minor variant on the bushy 

 growth of the Beindeer Moss (C rangiferina, erect and as much as 

 1^ ft. high), presents a similar miniature 'arboreal' habit, as a 

 fruticose ground-form, with main trunk and laterals; but (1) the 

 main axis is hollow, and has no skeletal strand, also it may be per- 

 forated locally, as at the axils ; the primary laterals are somewhat 

 irregularly spaced, though more definitely in acropetal series ; ultimate 

 ramuli acquire a more or less dichotomous habit, which may be veiy 

 pronounced in minute end-ramifications on which the apothecia are 

 borne. Lateral systems, again, may take on a distinct unilateral or 

 drooping habit: the larger types are bushy masses 1-1 i ft. high. 



