232 SUMMARY OF CURRENT RESEARCHES RELATING TO 



take part in the process of fertilisation. The sexual elements which 

 unite in any given case are generally derived from one and the same 

 individual, often from the same filament ; in Basidiobolus they are derived 

 from adjacent cells. 



In the higher Fungi, nuclear fusions occur at a definite stage in the 

 life-cycle, resulting in the production of spores, either directly (Ustila- 

 ginese, Urediueae) or indirectly (Ascomycetes, Basidiomycetes). These 

 nuclear fusions are probably not morphologically sexual ; but they re- 

 place the sexual act, and are physiologically equivalent to it. Among 

 the higher Fungi, the simpler Ascomycetes only, such as Sphtjerotheca , 

 exhibit a true sexual fusion, accompanied by a subsequent fusion of 

 nuclei in the ascus. 



Cell-division in Sporanges and Asci.* — Prof. R. A. Harper gives a 

 summary of recent researches on the various modes of cell-division in the 

 different families of Fungi, followed by the results of his own observa- 

 tions especially on Synchytrium, Pilobolus, Sporodinia, and Lachnea. The 

 following is a summary of his more important conclusions. 



There is a marked difference in the method of spore -formation in 

 the ascus and in the sporauge. In the ascus, as in the higher plants, 

 the cutting out of the daughter-cell from the mother-cell is effected by 

 the agency of the same fibrous kinoplasmic elements as were concerned 

 in the division of the nucleus. In the higher plants the flat cell-plate 

 is formed by the " cone principal " of the karyokinetic figure (as named 

 by Van Beneden) ; while in the ascus the daughter-cell is cut out of 

 the protoplasm of the mother-cell by an ellipsoidal plate formed from 

 the fibres of the antipodal cone. In this process the daughter-cell is cut 

 out of the interior of the protoplasm of the mother-cell, so that it remains 

 surrounded on all sides by the material of the mother-cell. The 

 daughter-cells do not contain all the protoplasm of the mother-cell, a 

 considerable mass remaining in the so-called " epiplasm." In all the 

 sporanges studied the cleavage is from the surface of the protoplasm or 

 from the surface of vacuoles of the mother-cell. The daughter-cells 

 are thus separated by cleavage-furrows, and the nature of the division 

 from the surface inwards precludes the possibility of the formation of 

 an epiplasm. 



Prof. Harper corrects his previous statement that the one-celled 

 ascospore is always uninucleate ; he has since found ascospores in which 

 nuclear division has occurred without cell-division. 



The present researches do not settle the question of the origin of 

 the Ascomycetes, but render it impossible to assume any very direct 

 relationship between the Phycomycetes and the Ascomycetes. 



Prof. Harper proposes to limit the term " free cell-formation " to the 

 process which takes place in the ascus. The method of division by which 

 the sporangiospores and conids are formed may be termed " cleavage by 

 constriction " ; and where the division proceeds to the ultimate separa- 

 tion of the energids as protospores, the process may be called " pro- 

 gressive and complete cleavage." 



Inheritance of an acquired Character in a Fungus, f — Prof. L. 

 Errera believes he has found evidence of this phenomenon in cultures 



* Aim. of Bot.. xiii. (1899) pp. 467-525 (2 pis.), 

 t Bull. Acad. Roy. Belgique, 1899, p. 81. 



