LYCOPODIACE^. 



[ 407 ] 



LYCOPODIACEiE. 



nella apoda for example, the corresponding 

 leaves of the pairs are unequal, and are so 

 arranged that the smaller he in two conti- 

 guous vertical rows, on the front of the stem, 

 ^ery much resembling the amphigastria of 

 Uypopterygium and some of the Jiinger- 

 nannice. In most of the Ljcopodiaceae the 

 eaves are simple and almost sessile ; but in 

 Tmesipteris they have a blade developed 

 nto two lobes, and borne on a long stalk ; 

 md in Psilotiim the short, scale-like leaf is 

 dso divided into two lobes and supported on 

 I petiole. The leaves of Isoetes are again 

 iifferent, consisting of long, quill-like bodies 

 )f a delicate structure, composed of large 

 Jells ; these are aquatic plants with very pecu- 

 iar habits and characters (see Isoetes). 



The reproduction of the Lycopodiaceae, 

 ipon which much light has recently been 

 hrown, is very curious; it is only accurately 

 mderstood as yet, however, in the genera 

 Selaginella and Isoetes, in which, as above 

 ;tated, two kinds of spores are known to 

 !xist. It is found that when both kinds of 

 ipore are sown, the results of their germina- 

 ion are totally distinct. The small dust- 

 ike spores burst their outer coat after a 

 ime, and the delicate inner membrane, 

 vhich is protruded, likewise bursts after a 

 ime and discharges extremely minute cel- 

 ules, in each of which is developed an 

 ictively moving spiral filament (spermato- 

 ;oid) like those of the Ferns. This breaks 

 )ut and swims about rapidly in the water 

 vhen seen beneath the microscope. 



The large spore exhibits no external 

 ;hange for a period varying from a few 

 veeks to a few months, but a section shows 

 hat a process of cell-formation has com- 

 nenced in its interior, which results in the 

 production of a kind of disk of cellular 

 ;issue in the upper part, beneath that por- 

 ;ion of the outer spore-coat which exhibits 

 ;he three converging ridges produced by the 

 pressure of the four spores in the parent-sac 

 luring their development. At this period 

 ;he spore appears to have three coats, an 

 )uter tough, coloured coat, a second coat 

 ining this, and a third which lines the 

 second over the great cavit)'^ of the spore, 

 3ut at the upper part invests the inside of 

 :he newlv-formed disk of cellular tissue, 

 A'hich thus lies between the second and 

 :hird coats. This disk of tissue is a pro- 

 ^.liallium analogous to the green body deve- 

 ioped from the free spores of the Ferns 

 md Equisetace^. On its upper surface 

 \rc developed a number of archegones of 



very simple structure. A cell of the sub- 

 stance of the prothallium taking on the 

 function of an e7iibryo-sac developes a free 

 cell {emhryo-cell) in its interior, and the cells 

 between this and the surface become modi- 

 fied, and part so as to leave an intercellular 

 canal between the contiguous angles of four 

 adjoining cells, leading down to the embryo- 

 cell, the four cells growing up from the 

 surface so as to form a kind of perforated 

 cellular papilla, something like that of the 

 archegone of the Ferns. At a certain stage 

 of this development, the outer coat of the 

 spore bursts at the converging ridges, and 

 the angular flaps resulting tm-n back and 

 expose the prothallium on the upper surface. 

 One (sometimes two, but as an irregularity) 

 of the embryo-cells is then fertilized by the 

 spiral filaments produced by the small spores 

 {pollinic sjjores), if these exist at the 

 right stage of the development in the vici- 

 nity. After this, the embryonal cell under- 

 goes multiplication, first growing down as a 

 cellular filament which breaks through into 

 the great cavity of the spore, the lower end 

 lying there then increasing until it acquires 

 the form of a cellular nodule, which breaks 

 out above and exhibits on its free portion 

 the first adventitious root and the first pair 

 of leaves ; the rootlet makes its way down- 

 wards into the soil, and the leaves are gra- 

 dually elevated on a thread-like stalk, and 

 separate, displaying two terminal buds 

 between them, whence the first bifurcation 

 of the stem proceeds. 



This mode of reproduction allies the family 

 very closely to the double-spored Marsi- 

 leaceae, and separates them from the Ferns 

 and Equisetacese, in which the prothallium is 

 formed outside the spores, from the single and 

 only kind which these plants jDOssess. But 

 a difficulty still exists with regard to those 

 species of Lycopodieae in which only the 

 smaller kind of spore has been met with, 

 such as our common Lycopodium clavatum, 

 inundatum, &c. No one has yet been able 

 to make these germinate ; and it is conjec- 

 tured by Hofmeister that they may possibly 

 produce a prothallium in their interior which 

 may bear both archegones and antherids, 

 like the extra-sporous prothallium of Ferns. 



The order Lycopodiaceae is divided into 

 tw^o families, in accordance with the struc- 

 ture of the sporanges. 



Families. 



I. Lycopodieee. Sporanges simple, one- 

 celled. 



