LYCOPODINEAE. HOMOSPOROUS LYCOPODIACEAE. 



275 



observer who has succeeded in seeing the first stages in the development of the 

 prothallium of Lycopodium immdatum. The exosporium opened by three valves and 

 the endosporium protruded in the form of a spherical vesicle ; the germ-tube divided 

 by a transverse wall into an inner basal cell, which suffered 

 no further change, and an outer, which developed as an 

 apical cell and formed two rows of segments. Each segment 

 divided by a tangential (periclinal) wall into an inner and an 

 outer cell, so that the young prothallium had now an axile 

 row of four short cells and round them two rows of lateral 

 cells and the basal and apical cells ; no further stage of 

 development was -obtained. It was not till fifteen years after 

 this, namely in 1872, that Fankhauser found fully developed 

 prothallia of Lycopodium annotinum among some mosses in 

 Switzerland, one of them being still connected with the 

 young plant f the second generation (Fig. 226). These 

 prothallia, which had grown in the dark, were yellowish white 

 masses of tissue with cushion-like lobes and a few small 

 rhizoids; they had a number of antheridia entirely sunk in 

 the tissue of the upper surface, forming ovoid cavities covered 

 over by a single layer of the cells of the prothallium (compare 

 Marattia), and containing a large number of the mother- 

 cells of spermatozoids ; the form of the spermatozoids them- 

 selves was not clearly made out. As these prothallia bore 

 no archegonia but had young plants growing from them, it 

 follows that Lycopodium has but one kind of spores, which 

 agrees perfectly with the results of direct observation, and 

 that the prothallia are monoecious ; by this latter character 

 the Lycopodiaceae are at once clearly distinguished from the 

 Selaginelleae and Isoeteae, and also by the large size of the prothallium which lives 

 entirely outside the spore. It is probable that the other genera with spores of one 

 kind only, Phylloglossum, Psilotum, and Tmesiplen's, have similar prothallia. The 



FlG. 226. Lycopodium an- 

 notinum ; p the prothallium, / 

 the young plant, w the root of 

 the plant, nat. size. After Fank- 

 hauser. 



cylindrical portion and beneath the crown of lobes antheridia and archegonia seem sunk in the 

 monoecious prothallium. The antheridia resemble those described by Fankhauser in L. annotinum, 

 and are like those in Marattiaceae and Ophioglossaceae. They arise from a single peripheral cell, 

 which divides into an outer lid-cell (subsequently divided by vertical walls into three cells) and an inner 

 cell within which the spermatozoids are formed. The form of the spermatoeoids is not certainly ascer- 

 tained ; probably they have only two cilia as in Selaginclla. The archegonia have very short necks of 

 three tiers of cells ; no basal cell is formed in their production and there is no special wall-layer round 

 the oosphere. At an early period the product of the division of the oospore consists of a massive 

 foot connecting with the prolhallium, a cylindrical mass of tissue, in the anterior end of which a 

 cotyledon is differentiated, whilst the posterior portion, rounded at the end and there usually 

 provided with a few hairs, shows no differentiation into members and is termed by Treub the 

 'embryonic tubercle.' There is no primary root; subsequently a root is developed laterally 

 and internally on the embryonic tubercle. Treub calls attention to the resemblance between 

 the young sporophyte and the young oophyte. In the cells of the primary tubercle of the oophyte 

 endophytic Fungus-hyphae are found so commonly that Treub is tempted to suggest a possible 

 commensalism, and it may be noted that Bruchmann found bodies like swarm-spores of Chytridieae 

 in the prothallia which lie examined.] 



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