148 ME. J. G. BAKER ON ALOINEiE AND YUCCOIDE^. 



proposed by Dr. Vines is a very reasonable one when considered 

 in the light of what apparently takes place in lichens. As Prof. 

 Lankester points out in the same article, " Light which has tra- 

 versed a solution of chlorophyll is still efficient in exciting the 

 plant-cell (whatever part of the cell may be called into play) to 

 the decomposition of C0 2 and the liberation of O." 



This proposed experiment appears to me to be proceeding natu- 

 rally in lichens. We have in them the fungal tissues, as the body 

 of the thallus and the chlorophyll screen, in the gonidial layer ; 

 that is, the chlorophyll is in one system of cells and the proto- 

 plasm apparently affected by it in another which is in contact. 

 The light which traverses the chlorophyll-containing gonidial 

 layer excites in the fungal tissues the decomposition of carbonic 

 acid. In evidence of this I would point to the plentiful occur- 

 rence of starch, or rather lichenin, a substance of the same che- 

 mical composition as starch (C 12 H l0 O 10 ), and formed from it, 

 according to Masche (Journ. prakt. Chemie, lxi. p. 7), by the 

 action of the free acids of the plant. Further, I venture to submit 

 that this process tends to explain the nature of the consortism 

 of the fungal and algal elements in the autonomous lichen, and 

 to support the well-known views of Schwendener *. 



A Synopsis of Aloinecc/tLnd Yuccoidece. 

 By J. G. BakWr, P.E.S. 



[Read January 15, 1880.] 



I have now come to that portion of my monograph of Liliaceae 

 that deals with the Aloes and Yuccas, a set of plants well known 

 in gardens, but which, from their large size and often succulent 

 character, are represented very sparingly in herbaria, and have 

 been almost totally passed over by travelling collectors of dried 

 specimens. They fall sharply into two tribes, which are marked 

 by well-defined botanical characteristics, which are correlated 

 with a completely different geographical dispersion. Of the 

 Aloes, which are characterized by their gamophyllous perianth 

 and thick fleshy leaves, there are nearly two hundred species, which 

 are strictly confined to the Old "World. Of the Y uccoidese, which 



* " Untersuchungen iiber den Flechtenthallus," in Nageli's ' Beitrage zur 

 wissenschaftlichen Botanik,' 4te Heft, 1868. 



