66 THE THALLUS OF THi!: GENUS PAEMELIA, 



mata, or loose and embedded in the gelatinous substance, or 

 ejected from the sperm agonium in myriads, and still im- 

 mersed in the same gelatinous substance. 



7. Alliances toith other Genera. 



The great lichenologist, Nylander, made his classifica- 

 tion depend mainly on the thallus, the apothecia and the 

 spermagonia,. On p. 57 of the Synopsis, he says, "Toutes 

 le.s parties des Lichens, le thalle, les apothecies et les sper- 

 magonies, jDeuvent offrir des caracteres servant a la> distinc- 

 tion des especes, et tantot c'est I'une, tantot I'autrei de ces 

 parties; qui decide le diagnostic dans des cas aanbigus. Mais 

 lorsqu'il s'agit des lichens inferieurs, il faut avoir recours 

 ail microscope pour chercher dans la texture des tissus et 

 la conformation des elements, soit du thalle, soit du fruit 

 ou des spermagonies, les signes qui caracterisent les especes. 

 Ou ne doit cependant pas oublier que les caracteres micro- 

 soopiquciS, dans certain especes, sont aussi sixjets a verier 

 que les autres. Ainsi le nombre des spores dans les theques, 

 le nombre des cloisoais dans les spores, la couleur de 

 ces dernieres, leur grandeiur, varient souvent dans lee 

 eepecesi polymorphes, tandis que ^lesi imemesi caracteres 

 offrent une grande fixite dans d'autres. Les spermaties et 

 leurs sterigmates serviront aussi quelquefois a la distinc- 

 tion des formes douteuses ou des echantillons manquant 

 de fruits." 



Of these tests for specific and generic differences that 

 of the spemiatia and sterigmata has, since Nylander's 

 time, fallen out of use. In the last great work on Lichen- 

 ology — "A Monograph of the British Lichens, Part II. , by 

 Annie L. Smith," published by the authorities of the 

 British Museum, although the cha.racters of the speirmatia 

 are given for the ordersi, and generally for the genera, there 

 is seldom a refereucei to these organs in the specific descrip- 

 tions, even when, as in the characteristics of the genus 

 Lecidea, p. 10, the spemiatia are described as "acicular, 

 straight, rarely arcuate or shortly cylindrical." 



In the Monograph referred to above the classification 

 does not lean greatly on the symbiosis of alga and fungus, 

 for though the gonidia are spoken of throughout as "algal 

 cells," yet such statements are common as p. 206, "algal 

 cells, Trentepohlia or Palmellacese/' p. 275, "algal cells, 

 Pleurococcus or Palmella,/' etc. 



In this extremely important work the classification 

 depends almost wholly on the microscopic structure of the 

 fruit. As Miss Smith states in her Introduction, 'More 



