New Palceozoic Lycopod with a Seed-like Structure. 473 



4. Certain phenomena of precipitin reactions, including precipitation, 

 inactivation, inhibition, and solution of precipitates, appear to be incompatible 

 with the commonly accepted statement of Ehrlich's theory of the substances 

 concerned in precipitin interactions. 



Miadesmia membranacea, Bertrand ; a New Palceozoic Lycopod 



with a Seed-like Structure. 



By M. Benson, D.Sc, F.L.S. 



(Communicated by Dr. D. H. Scott, F.E.S. Received April 26, — Read 



June 13, 1907.) 



(Abstract.) 



The vegetative organs of this interesting new type were discovered by 

 Bertrand in 1894. He found them in sections of a calcite nodule from the 

 Gannister beds of Hough Hill, England. A large quantity of new material 

 has become available, and now not only are more details known as to the 

 vegetative organs, but a fairly complete knowledge of the reproductive organs 

 is possible. 



Miadesmia was exceedingly minute, its stem slender and without any trace 

 of skeletal tissue. It is the first . Palaeozoic Lycopod of herbaceous character 

 known structurally. The megasporophylls which were identified by 

 Dr. D. H. Scott, F.R.S., in 1901, show a more advanced type of seed habit 

 than has hitherto been met with in Cryptogams. The megasporange gives 

 rise to but one thin-walled spore, which in development and structure 

 resembles an embryo sac and germinates in situ. An integument surrounds 

 the sporange, leaving but a small orifice as micropyle. This is surrounded by 

 numerous long processes of the integument, which formed a collecting and 

 incubating apparatus for the microspores. There is no trace of an envelope 

 about the microsporange. The carpellary leaf was shed at maturity, and 

 resembles a winged seed. 



Disregarding the structural modifications of the megasporophyll, the 

 nearest affinity of Miadesmia among forms so far known seems to be with 

 the non-specialised species of Selaginella, such as Selaginella selaginoides, but 

 the foliage leaves show the archaic leaf-base comparable with that of 

 Lepidodendrese. 



