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TWO TYPES OF DOUBLPJ-CELLED STRUCTURES. l7 



there is only one, might ulso have been accepted as proving that con- 

 jugation had tal^en phice. This does not mean, of course, that cross- 

 fertilization is indispensable for spore production among the fungi, 

 but their habits of growth certainly give many opportunities for con- 

 jugations between m3^celia of different descent, by which the existence 

 of compact and well-defined species can be maintained, although the 

 peculiar structure of fungous tissues permits extreme variability of 

 the size and external form of the fruiting bodies. 



In structural complexity, size, longevity, and other measures of 

 organic efficiency the biiuicleate fungi have an intermediate position 

 in the plant series. Their wide distribution and extensive ditieren- 

 tiation into species, families, and orders are evidences of ample oppor- 

 tunities in time and environment, so that it is not unfair to explain 

 their evolutionary limitations by reference to their peculiar type of 

 organic structure. 



Sexual reproduction is accomplished through conjugation or fusion 

 of cells, a process which may be divided into three stages: (1) Plas- 

 mapsis, the fusion of the cytoplasm or unsppcialized protoplasm; 

 (2) karvapsis,'' the fusion of the nuclei or nuclear protoplasm; (3) 

 synapsis, the fusion of the chromatin. The binucleate cells of the 

 fungi may be said to have passed the stage of plasmapsis, but kary- 

 apsis, or true fecundation, like that of the higher plants and animals, 

 has not taken place. 



For the form of sexuality which produces the binucleate cell struc- 

 tures of the higher fungi the nsune aj)(fi//oga7)iy \h proposed, in allusion 

 to the fact that the two nuclei have not yet associated. The higher 

 stage, where the nuclei fuse but the chromosomes remain apart, may 

 be c'd\\edj)<fra(/ami/^ which implies that the union is still incomplete, 

 but that a more intimate relation has been established. These two 

 double-celled conditions may be further contrasted with haplogamy^ 

 the primitive method of undef erred combination of the sexual cells, 

 nuclei, and chromatin. 



To the ''asexual generation," which is not asexual and not a gener- 

 ation, the term paragamic phase may be applied among the higher 

 plants and animals, the tissues of which are composed of cells with a 



" The etymology of these terms will be obvious to all students of biology, plumia 

 and A;aryon being the familiar Greek renderings of protoplasm and nucleus, respec- 

 tively. The other element, cxi^i'i, signifies a binding or tying together and also a 

 mesh or network, a meaning especially appropriate in view of the reticular struc- 

 ture of living matter. 



The series might be completed more logically by using the distinctive word 

 mitapsis as a substitute for synapsis, which in its etymology is scarcely more than a 

 Greek ecjuivalent for the general term conjugation. Mitapsis is derived from /liroi, 

 a thread, and alludes to the threadlike condition assumed by the chromatin during 

 the process of chromatic fusion. 



