674 SUMMARY OF CURRENT RESEARCHES RELATING TO 



the 6telic cells, which number only three. These three stelic cells after- 

 wards divide to produce the sieve-tubes, the vessels, and the conjunctive 

 of the definite stele ; but no pericyclic region can at any time be dis- 

 tinguished. 



In the root of Azolla there is a pericyclic layer outside the two 

 xylem-bundles, each of which is composed of two vessels. The outer 

 of these vessels undergoes differentiation before the sieve-tubes, — a 

 speciality of this root. 



In Ferns, the first layer detached at the periphery of the stele re- 

 garded as the pericycle, gives rise to the first sieve-tubes. Some of 

 these cells divide by a tangential septum, and the inner daughter-cells 

 develop into sieve-tubes, while the outer daughter-cells gradually 

 acquire the dimensions of the undivided pericyclic cells. Additional 

 sieve-tubes are afterwards differentiated directly within the undivided 

 pericyclic cells ; they are situated on the same arc as the first sieve- 

 tubes ; so that the two kinds of sieve-tube cannot afterwards be dis- 

 tinguished. 



Sporange and Inflorescence of Selaginella.* — According to Prof. 

 K. Goebel, the impregnation of the female by the male organs on the 

 same spike in Selaginella is rendered difficult by their relativo position ; 

 by the proterogyny of the sexual organs ; by the violent expulsion of 

 the megaspores when ripe ; and by the unequal rapidity of germination 

 of the two kinds of spore from the same spike. The two kinds of 

 sporange open in the same way, viz. by two valves which become de- 

 tached, by lateral fissures, from the basal boat-shaped portion ; but, in 

 the megasporange, the mechanism for the expulsion of the spores 

 renders the structure of the wall the most complicated that occurs in 

 Pteridophytes. In no other genus of Pteridophytes is there a mechanism 

 for the mechanical expulsion of spores. 



The inflorescence (BluthenstancP) presents the only example of a 

 dorsiventral arrangement in these organs that occurs in Pteridophytes ; 

 it is in Selaginella the most common arrangement of the vegetative 

 organs. 



Imperfect Sporanges in Pteridophyta.f — Prof. F. O. Bower dis- 

 cusses the question whether the imperfect sporanges found in certain 

 Vascular Cryptogams are vestigial. The instances cited occur especially 

 in many species of Lycopodium, though illustrations are given from other 

 genera and from fossil plants. A discussion of the phenomena of de- 

 velopment leads the author to the conclusion that the imperfect spor- 

 anges at the base of the strobile are vestigial organs, and are not 

 indicative of an upward evolution, leading in the race to the complete 

 sporange. In Lycopodium there appears to be a zone of reproductive 

 activity, limited below by phylogenetically evanescent or vestigial parts, 

 above by phylogenetically nascent or supernumerary parts. 



Anatomy of the Schizaeaceae.J — The following is given as a sum- 

 mary of the more important results derived from an examination by 

 L. A. Boodle of the structure of a number of species of Schizaeaceae 

 belonging to the genera Lygodium, Sehizaea, Anemia, and Mohria. 



* Flora, lxxxvui. (1901) pp. 209-28 (16 figs.). 



t Ann. of Bot., xv. (1901) pp. 225-67. J Tom. cit., pp. 359-421 (3 pis.). 



