230 



REPRODUCTION, VEGETABLE (VEGETABLE OVUM). 



of elements : first, the paraphyses, which are 

 linear, claviform filaments, composed of from 



Fig. 152. 



Section of fruitful thallns of Sticta pulmonacea, 

 about 20 diam. 



a, discoid apothecium. The vertical lines indicate 

 the lamina proligera ; s, spermogouia containing 

 sperniatia ; i, empty spermogonia. 



six to eight cylindrical cells, joined end to 

 end; and secondly, the thecce, which are 

 obovate vesicles, each containing, almost in- 

 variably, eight spores. These elements are 

 arranged side by side, their long diameters 

 being perpendicular to the surface of the 

 apothecium. They appear to be glued toge- 

 ther, even in the fully formed apothecia, by 

 an intermediary gelatinous substance, which, 

 however, there is good reason for supposing 

 to be nothing more than a thickening of 

 the external membrane, from which it cannot 

 be distinguished, either in respect of its 

 chemical or other characters. Iodine colours 

 this substance, as well as the external mem- 

 branes of thecae and paraphyses, blue, 

 without the addition of sulphuric acid. In 

 the early condition, the cavities of the thecas 

 are occupied by a yellow, plastic material, 

 out of which the spores are afterwards formed. 

 The thickness of the external starchy mem- 

 brane is at this period relatively more consi- 

 derable than later ; as the spores increase 

 in size, it gradually diminishes. The struc- 

 ture of the fully formed spore is best ob- 

 served in those species in which it is largest. 

 The spore-membrane, of considerable pro- 

 portional thickness, is smooth and semi- 

 transparent, wholly unaltered by iodine and 

 sulphuric acid. The contents consist partly 

 of mucous granules, which are coloured 

 brown by iodine, partly of yellowish oil 

 globules. The whole is usually invested, even 

 after its escape from the theca, with the 

 still adherent remains of the inner proto- 

 plasmic layer, by which it was immediately 

 surrounded. In form, the spores are most 

 frequently ellipsoid and unilocular. In other 

 instances, however, they are divided by one 

 or more partitions. This division is either 

 complete, so that the spore resembles two 

 obovate cells joined by their larger ends ; or 

 incomplete, the septa being in some cases 

 scarcely distinguishable from the protoplasmic 

 contents of the central cavity. 



47. The spores are discharged from the 

 theca3 with an elastic force often sufficient to 

 project them to a considerable height above 

 the surface of the apothecium ; a fact, which 

 M. Tulasne seems lo have shown to be 



dependent on the great capability of imbibing 

 moisture possessed by the lamina proligera, 

 which much exceeds that of the tissue imme- 

 diately subjacent. It resembles altogether 

 what is observed in the Pezizas, whose spores, 

 it is well known, are projected with such 

 force as to form a cloud above the receptacle. 

 48. We have next to notice the remarkable 

 organs which Itzigsohn* described as the 

 antheridia of the Lichens, and to which he was 

 the first to assign a distinct function. They 

 had been previously adverted to by several 

 botanists, and had been usually considered as 

 parasitical Pyrenomycetes, which they closely 

 resemble. They consist of conceptacles em - 

 bedded below the upper surface of the thallus ; 

 their presence is revealed by the appearance 

 of blackish, projecting points, scattered at 

 irregular intervals. The form of these organs, 



Fig. 153. 



Spermogonia of Scittula Wallrothii, 150 diam. 



The sperniatia are seen escaping in numbers 

 from the apicial aperture of the organ. 



which MM. Tulasne have named spermo- 

 goniaB, is globular, ellipsoid, or oblong. Their 

 external envelope is frequently hard and 

 crustaceous, and usually blackish. The cavity 

 may be simple or multiple ; in the latter case 

 all the compartments or sinuses open at one 

 ostiole. The whole of the cavity is occupied by 

 a filamentous tissue, which consists of two 

 elements viz., spermatia and the organs on 

 which they are supported. The latter are 

 simple or branched filaments, which are usu- 

 ally undivided, but occasionally jointed. They 

 originate from the inner surface of the con- 

 ceptacles. At their summits and articulations, 

 they bear the spermatia, which are straight or 

 curved linear organs of great tenuity, and 

 are motionless. They are coloured brown by 

 iodine ; both the spermatia and filaments are 

 embedded in an abundant mucilage ; many of 

 the former are sterile, and are so long that 

 they project beyond the opening of the con- 

 ceptacle like a kind of cirrhus. The whole 

 structure corresponds in every respect with 

 that of the spermatia-bearing conceptacles of 

 the Discomycetes and Pyrenomycetes. 



49. To a third variety of conceptacle, MM. 

 Tulasne have assigned the title of pycnidis, 

 This organ, although it has only been ob- 

 served in two genera, Abrothallus and Scutula, 



* Bot. Zeitung. 1850. S. 913. 



