LYCOPODIACE^. 



[ 407 ] 



LYCOPODIACEJL 



nella apoda for example, the corresponding 

 leaves of the pairs are unequal, and are so 

 arranged that the smaller lie in two conti- 

 guous vertical rows, on the front of the stem, 

 very much resembling the amphigastria of 

 Hypopterygium and some of the Junger- 

 mannice. In most of the Lycopodiaceae the 

 leaves are simple and almost sessile ; but in 

 Tmesipteris they have a blade developed 

 into two lobes, and borne on a long stalk ; 

 and in Psilotum the short, scale-like leaf is 

 also divided into two lobes and supported on 

 a petiole. The leaves of Isoetes are again 

 different, consisting of long, quill-like bodies 

 of a delicate structure, composed of large 

 cells ; these are aquatic plants with very pecu- 

 liar habits and characters (see ISOETES). 



The reproduction of the Lycopodiaceae, 

 upon which much light has recently been 

 thrown, is very curious; it is only accurately 

 understood as yet, however, in the genera 

 Selaginella and Isoetes, in which, as above 

 stated, two kinds of spores are known to 

 exist. It is found that when both kinds of 

 spore are sown, the results of their germina- 

 tion are totally distinct. The small dust- 

 like spores burst their outer coat after a 

 time, and the delicate inner membrane, 

 which is protruded, likewise bursts after a 

 time and discharges extremely minute cel- 

 lules, in each of which is developed an 

 actively moving spiral filament (spermato- 

 zoid)like those of the FERNS. This breaks 

 out and swims about rapidly in the water 

 when seen beneath the microscope. 



The large spore exhibits no external 

 change for a period varying from a few 

 weeks to a few months, but a section shows 

 that a process of cell-formation has com- 

 menced in its interior, which results in the 

 production of a kind of disk of cellular 

 tissue in the upper part, beneath that por- 

 tion of the outer spore-coat which exhibits 

 the three converging ridges produced by the 

 pressure of the four spores in the parent-sac 

 during their development. At this period 

 the spore appears to have three coats, an 

 outer tough, coloured coat, a second coat 

 lining this, and a third which lines the 

 second over the great cavity of the spore, 

 but at the upper part invests the inside of 

 the newly-formed disk of cellular tissue, 

 which thus lies between the second and 

 third coats. This disk of tissue is a pro- 

 thallium analogous to the green body deve- 

 loped from the free spores of the FERNS 

 and EQUISETACE^E. On its upper surface 

 are developed a number of archegones of 



very simple structure. A cell of the sub- 

 stance of the prothallium taking on the 

 function of an embryo-sac developes a free 

 cell (embryo-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 turn 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 spores], 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 Equisetaceae, in which the prothallium is 

 formed outside the spores, from the single and 

 only kind which these plants possess. 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 

 two families, in accordance with the struc- 

 ture of the sporanges. 



Families. 



I. Lycopodiete. Sporanges simple, one- 

 celled. 



