EMBEYOGENY IN LICHENS. 



269 



support), (fig. 475). Besides the spermagones, other externally 

 similar reproductive bodies, oaWed pycnides (vumhg, crowded) (fig. 476), 

 are, though less regularly, produced on the thallus, containing minute 

 bodies denominated stylospores (fig. 477 i), which are either attached 

 to style-like stalks (basidia), a, or are found free, c. 



The fertilisation of Lichens is still very obscure, and the functions 

 of their several reproductive organs require further examination. In 

 the thallus of lichens there are interlaced filaments or threads, forming 

 what is called the hypha (fig. 474 /), (i/p^, weaving), in the midst of 

 which are peculiar green-coloured rounded bodies, called gorddia- (fig. 

 474 g) (yoKos, offspring, ilbgi, form), which appear to be concerned 

 in vegetative propagation, like the zoospores of Algse. These gonidia 

 have been shown in some cases, as in Parmelia parietina, to contain 

 corpuscles capable of development into zoospores. 



In the division of Thallogens called Algse, embracing Cryptogams, 

 ■which inhabit salt and fresh water, there are more evident organs 

 of fecundation. We have already noticed these in the case of the 

 conjugation of confervse (fig. 471), when two cells being difierent, the^ 

 contents unite to form a spore or germinating body. This process 

 is seen also in Diatoms and Desmidiese. In the minute Closterium 

 Lunula there is a fissiparous division of the plant, and the contents of 

 the two ruptured cells unite to form a rounded body, containing a 

 spore. Besides the process of conjugation, there are also other modes 

 of reproduction in Algse ; the same plant is seen forming cells which 

 separate as independent plants, and also antheridia and archegonia 

 which give rise to spores. In Vaucheria there 

 is a multiplication by zoospores or moving cells, 

 which are discharged from the extremity of a fila- 

 ment (fig. 478 a and h). This zoospore (fig. 478 

 6) is a vegetative reproductive body, independent of 

 fertilisation. The plant also produces a recurved 

 horn-like organ, which performs the part of an an- 

 theridium, and a slightly recurved organ close beside 

 it, which represents the sporangium, from which 

 a beak-like process is turned in the direction of the 

 antheridium. These two organs are then in direct 

 communication by their bases with the tube of the 

 Vaucheria, but they are afterwards separated from 

 it, each forming a septum. Spermatozoids, contained in the an- 

 theridium, afterwards penetrate the beak-like process of the spo- 



Fig. 478 a. Clavatecellularfilamentof^Alga(rawcAerm(M;oidea). The terminal portion 

 becomes .separated from the rest by a partition. In this portion the single spore, s, is de- 

 veloped, which is discharged through an opening, as seen in the figure. The spore has cilia, 

 by means of which it moves about for some time in water after being separated from the 

 parent cell. The lower part of the filament contains green endoohrome. The spore is of a 

 very dark gre'en colour. 2), Zoospore of an Alga {Vaucheria), surrounded by moving cilia. 



Fig. 478. h. 



