30 



PRINCIPLES OF PLANT-TERATOLOGY. 



which may be regarded as a reversion to the primitive 

 type (fig. 5). Cases in which the hymenium covers 

 the whole of the upper exposed surface, in the form 

 of a semi-alveolar structure, or labyrinthiform gill- 

 formation, are seen in Tremella and Nsematelia ; and 

 these plants pertain to the Protobasidiomycetes ; the 

 Tremellinese have, according to Maire's classification, 

 branched off laterally from the Auriculariaceae ; and 

 it is from these latter that the Agarics and Poly- 

 poracese have descended. 



Hence there is some support 

 for the view that the " morchel- 

 loid " forms of certain Agarics, 

 described above, are reversions, 

 for this very structure occurs in 

 some primitive forms of the same 

 great group. 



The highly differentiated cap of 

 Agarics and Polyporacese must be 

 a recent structure, in all proba- 

 bility derived from a " fruit " of 

 simpler construction, in which the 

 hymenial tissue was uniformly and 

 Hymenial tissue Tvmed generally distributed. 



on the side of stipe ; cap- Abnormal Conditions Of the Sub- 

 formation absent. (After . . -■ f> ft i 



Buiier.) stratum, sucn as excess ot iood, 



of the air, or of light, would tend 

 to upset the balance of the organism, and induce a 

 reversion or harking-back of the structure to a simpler 

 form. This involves the transformation of the sterile 

 tissue of the upper surface of the cap into the original 

 fertile tissue. The cap-like form is probably derived 

 from the cylindric by compression, and expansion in 

 the horizontal plane. In fact, we see this original 

 simple structure still retained in the otherwise complex 

 type of Phallus. This mode of origin of the "cap" 

 is also clearly shown by such an abnormality as that 

 seen by Buller in Lentinus (PI. II, fig. 1) where the 

 secondary stipes (s 2 ) are springing from the edges of 



