22 THE JOURNAL OF BOTAIs^Y 



COCCUS viridis Ag., as defined by AVille, is rarely the gonidium of 

 British lichens, as vegetative division by true " cloisonnement " is 

 seldom seen within the thallus. 



In the section describing the reproductive organs, four illustra- 

 tions show the structure of apothecia and perithecia as seen in trans- 

 verse section. These should prove helpful to the student, as they 

 illustrate the essential points to be considered when a genus is being 

 determined by the structure of the reproductive organs. 



In the section Ecology and Distribution, reference is made to a 

 specimen of Parmelia saxatilis, kept under observation for a con- 

 siderable time, which increased in diameter on an average of one 

 centimetre in a year. This probably represents the average increase 

 in diameter of a large number of foliose lichens, but sometimes 

 growth is more rapid : this is the case with Feltigera spuria, which 

 often makes an appearance on burnt portions of heath land at the 

 time when the moss Funaria hygrometrica, Avhich first occupied the 

 burnt patch, shows signs of exhaustion. The branchea of the thallus 

 of this lichen grow from 2 to 3 cm. in from six to eight months. 

 Lecaiiora saxicola has been observed to grow 2-5 cm. within the same 

 period. 



The chief characteristics of Phylogeny and Classification are 

 tabulated and concisel}' described. \Ye welcome the method intro- 

 duced in this volume of giving measurements of spores and spermatia 

 in mikrons rather than in fractions of millimetres, as being simpler 

 and clearer than that previously employed. The warning that 

 chemical reactions cannot always be relied upon will save the amateur 

 a certain amount of hesitation and uncertainty when dealing with 

 specimens that require critical determination. 



Comparison with the first edition shows that the subject of 

 classification is now approached from a different standpoint. The 

 structure of the reproductive organs has become the touchstone ; 

 British lichens are accordingly arranged in two series, Gymnocarpecd 

 and PyrenocarpecB ; the former including the subseries Coniocarpinece^ 

 CycJocarpinecs, and GrapJiiclinecB. 



Each order is provided with a key to the genera. The list of 

 synonyms following the diagnosis of a species has in many cases 

 received additions, and the record of localities shows a wider distribu- 

 tion than was previously indicated. The restriction of general habitat 

 has been occasionally removed ; thus Calicium hyperellum "in upland 

 wooded districts" (ed. 1, p. 91) now reads (p. 18) "in Avooded dis- 

 tricts." This recognises a considembly greater latitude in distribution 

 and accords with the actual facts. The sequence of orders and the 

 inclusion, or otherwise, of genera within their limits afford ample 

 evidence of independent opinion and of the exercise of a mature 

 judgement based upon laborious microscopic examination of large 

 numbers of specimens. There is a wide divergence of view as to the 

 genera -that should be included in JJsneacecB. In this w^ork the 

 following are given as comprising the order : — Evernia, Bamaliua, 

 Jlsnea, Alectoria, and Cerania {Thamnolia). Zahlbruckner (1901) 

 omits Alectoina, while Hue (1901) does not include Evernia; 

 Harmand (1907) includes Teloschistes and Jatta (1909) adds Cetraria 



