404 Anatomie. — Cytologie und Befruchtung. 



apical centres of growth were not met with at all. An ex- 

 haustive account of the anatomy is given which includes the 

 ioilowing points of special interest. The sieve-tubes are without 

 nuclei, and contain the refractive granules described by 

 Poirault as occurring in the sieve-tubes of so many ferns, 

 but no definite pores or sieve-plates were observed, and no 

 callus; nor could a definite protophloem be distinguished. In 

 the aeriai stem the phloem tissues may become more or less 

 lignified. At one point in the subterranean part of the erect 

 shoots the sclerotic fibres that occupy the centre of the xylem 

 in the upper aeriai region are replaced by parenchymatous 

 pith. Spiral protoxylem Clements occur in the aeriai stem but 

 not in the rhizome. 



In conclussion Professor Bo wer 's view that the sporangial 

 apparatus is a single septate sporangium is supported, and it 

 is held that, as a saprophyte, Psilotum probably represents a 

 much reduced form which may have retained some primitive 

 Characters. D. J. Gwynne-Vaughan. 



BlackmäN, V. H., On the relation of Fertilisation, 

 „Apogamy", and „Parthe nogenesis''. (New Phytolo- 

 gist. Vol. III. 1904. p. 149—158.) 



The author summarises the more important features of 

 fertilisation and discusses their relations to the processes invoked 

 in Apogamy and Parthenogenesis. He emphasises the signi- 

 ficance of fertilisation as a mean of securing: 1. Developmental 

 Stimulus, 2. amphimixis, 3. doubling the number of previously 

 reduced chromosomes. The nature of the Stimulus is briefly 

 discussed, and the conclusion arrived at is that it is chemical. 

 The value of exogamous conjugation of gametes derived from 

 different sources seems to rest on the assumed differences of 

 Constitution resulting from the circumstances of their origin. 

 But in-breeding may occur, and is common in those fungi, for 

 example, in which sexuality is on the decline. 



The examples of apogamy in certain fern prothallia, and 

 in uredineae are cited as cases in point. Instances of partheno- 

 genesis, such as that of Artemia lead on to those in which a 

 mere somatic budding replaces any fusion of actual or pseudo- 

 gametes. The examples of the more recently observed cases 

 of „parthenogenesis" in angiosperms are criticised, especially 

 in the light of the cytological difficulty that the egg possesses not 

 the gametophytic, but the sporophytic number of chromosomes. 



The latter part of the paper is devoted to consideration of the 

 nuclear mechanism in its relation to development, and the 

 general conclusion is reached that many of the abnormal 

 phenomena witnessed in the various processes rather loosely 

 included under the term „parthenogenesis", are the expression 

 of various expedients to enable the young organism to start 

 life with the somatic (unreduced) complement of chromosomes. 



B. Farmer (London). 



