VAUCHERIACE.E. 117 



B. Between the antheridia and thallus itself is found a shorter empty 

 boundary cell (not containing chlorophyll). 



a ANDROPHOEJE, Several horn-shaped bent antheridia placed 

 on a swollen cell containing chlorophyll, which is fixed to 

 the side of the thallus, by means of the boundary cell. 



12. V. synandra, Woron. 



1) PILOBOLOIDEJE. Antheridia bordering immediately on the 

 boundary cell (frequently provided with several mouths). 

 aa Oogonium borders immediately on the thallus branch. 

 * Several fructification tubes on the 

 oogonium. 



13. V. coroJiata, Nordst. 

 ** Oogonium with only one fructification 

 opening, but the antheridia with 

 several, 

 f Oospore round. 



14. v. intermedia, Nordst. 



15. V. gphcerospora, Nordst. 

 f f Oospore lens-shaped. 



16. V. piloboloides, Thur. 

 bb Below the oogonium a boundary cell. 



17. V. litorea, Hofm. 

 Place uncertain. 



18. Y. tuberosa, Br. 



11). V. trifurcata, Kutz. 



The sexual reproduction in Vaucheria has been minutely described by 

 Pringsheim, of which we give an abstract. Vaitcheria, besides the 

 asexual multiplication by zoospores also exhibits a true sexual propaga- 

 tion, effected by means of the two organs known as the " hornlets" and 

 the spores, the latter being more correctly termed " sporangium." Both 

 organs arise like papillary branches from the tube, and in close proximity. 

 It is usually the case that the papilla destined to become the hornlet is 

 formed sooner than that in which the sporangium originates. The two 

 papillge even from the first differ so widely in dimensions, that they can 

 scarcely be confounded. The papilla which becomes the hornlet soon 

 elongates into a short cylindrical slender branch, which at first rises 

 perpendicularly from the tube, then curves downwards until it comes in 

 contact with the tube, often forming a second, or a third curve, and in 

 this way always represents a more or less stunted branch, which fre- 

 quently exhibits several spiral turns. The papilla of the neighbouring 

 sporangium usually begins to appear at the time when the hornlet is 

 commencing its first turn ; but the period at which it arises is very 

 indeterminate, for it sometimes appears much earlier, whilst the hornlet 

 is still perfectly straight, sometimes much later after it has curved, so as 

 to form two limbs of equal length. 



The papilla destined to become the sporangium gradually enlarges 

 into a considerable-sized lateral out-growth of the tube, far exceeding the 

 hornlet in width, whilst in length it is barely equal to the straight limb 

 of the latter. This out-growth which is afterwards symmetrical, 

 ultimately throws out a beak-like prolongation on the side looking 

 towards the hornlet, the rostrum of the sporangium, whence the latter 

 acquires its peculiar form, resembling that of a half developed vegetable 

 ovule. Up to this period the hornlet as well as the sporangium are not 

 shut off from the tube by any septum ; the cavity of the hornlet and that 

 of the sporangium consequently remain uninterruptedly continuous with 

 the parent tube, and are filled with similar contents. A number of 

 chlorophyll granules in an albuminous plasma and rounded oil globules, 

 constitute a dense lining to the tube, the sporangium, and the hornlet. 

 Between this and the cellulose membrane is the thin colourless cutaneous 

 layer. 



