Botrydiacece 



259 



j\A 



change of conditions usually resulting in a corresponding variation 

 in the reproductive process. These different processes have been 

 worked out by Rostafinski 

 and Woronin 1 and the 

 final result is in each case 

 either the production of 

 zoogonidia or aplano- 

 spores. The zoogonidia 

 are small and ovoid in 

 shape, with one or two 

 chroraatophores and one 

 long cilium. (Very pro- 

 bably there is a second 

 shorter cilium, but its 

 presence has not yet been 

 ascertained.) The whole 

 plant frequently becomes 

 a huge zoogonidangium, 

 especially if it becomes 

 submerged, and the zoo- 

 gonidia escape through 

 an apical opening. The 

 aplanospores, which are 

 globose or ellipsoid, often 

 become hypnospores, and they are frequently produced in numbers 

 in the rhizoids. On the green portion of the plant above ground 

 becoming too dry, the contents migrate into the rhizoids and a 

 large number of aplanospores are formed. The development of the 

 young plants varies much, depending upon the external conditions. 

 Rostafinski and Woronin described a sexual reproduction by 

 the conjugation of isogamous gametes, but Klebs has given good 

 reasons for doubting this. 



B. granulatum (L.) Grev. is a very local plant. It occurs widely distributed 

 over the British Islands, but the conditions are not often suitable for its 

 appearance above ground. It is found almost exclusively on drying-up mud, 

 and sometimes occurs in countless numbers on mud turned out from a canal 

 or on the drying bottom of a muddy pond. I have observed these plants so 

 thick as to stand out in mulberry-like masses from the surface of the damp 

 mud. The nature of the mud is immaterial and the Alga is not uncommonly 

 found on chalk mud. The plants reach a diameter of 2'25 mm. Fig. 122. 



Fig. 122. Botrydium granulatum (L.) Grev., 

 from Calverley, W. Yorks. A, nat. size; B and 

 C, x45; D and E, x450; D, aplanospores; E, 

 germinating aplanospore. 



1 Rostafinski & Woronin in Botan. Zeitung, xxxv, 1877. 



172 



