CLUB-MOSSES AND THEIR ALLIES. 131 



of the archegonium, and the upper of the two cells thus 

 formed develops into a suspensor, a structure characteris- 

 tic of flowering plants, but occurring in few- cryptogams. 



RELATIONSHIP. 



It is desirable that at least the external characters and 

 fructification of one or more additional genera of vascular 

 cryptogams should be studied in connection with the pre- 

 ceding ones ; but specific directions are omitted, partly 

 because of uncertainty as to material likely to be procura- 

 ble, and partly because it is understood that by this time 

 the student should be in a position to make an intelligent 

 comparative study of at least the general characters of 

 any group to which he has already given special attention. 

 Club-mosses are as likely to be available as any of the 

 Lycopodinese, since they are pretty widely distributed, 

 and besides are extensively used for Christmas decorations. 

 As they appear in market in the middle of winter they are 

 frequently in fruit. Marsilia and Isoetes are of great 

 interest, and when they can be obtained may well claim 

 a considerable share of the time given to this group. 

 Aside from the manuals and text-books, the references 

 given below will be found serviceable to those who under- 

 take a further study of the vascular cryptogams. 1 



1 Campbell, Development of Pilularia globulifem, L., Annals of 

 Botany, Vol. II, p. 233 ; Contributions to the Life-History of Isoetes, 

 Annals of Botany, Vol. V, p. 231 ; On the Prothallium and Embryo of 

 Osmunda Claytoniana, L., and 0. cinnamomea, L., Annals of Botany, 

 Vol. VI, p. 49 ; On the Affinities of the Filicinece, Botanical Gazette, 

 Vol. XV (1890), p. 1 ; On the Relationships of the Archegoniata, Botani- 

 cal Gazette, Vol. XVI (1891), p. 323. Frequent references to other 

 important literature are given by the author in the papers cited. 



