CUEEET ON GEKMINATION OF RETICULAEIA UMBEINA. 407 



them in this country. The writer there says that in the spores of 

 this species, one half (or nearly so) of the membrane is much more 

 delicate than the remaining portion, the line of demarcation between 

 the two portions being sharply defined. In all the spores of Beticu- 

 laria umbrina which I have examined, I find the membrane of one 

 uniform thickness. 



At the time when De Bary's observations were made, the exist- 

 ence of zoospores in fungi had not been ascertained, but they have 

 since been found to occur in the common white rust of the Cruciferse 

 (^Cystopus candidtis IjOy.), and hxFero)iospor a. 



Of course the discovery of zoospores in other fungi diminishes 

 the importance- of the fact of their existence in the Myxogastres, but 

 it is still a matter of considerable interest to ascertain whether the 

 phenomenon is general, for out of about 250 species of which the 

 tribe consists, the zoospores have as yet not been observed in more 

 than a dozen, a number hardly sufliciently large to justify the general 

 inference of uniformity in germination which De Bary seems inclined 

 to draw. 



I have lately had the opportunity of examining fresh specimens 

 oi Beticularia U7nbrina, and. of experimenting upon their germina- 

 tion. The spores are of a brown colour and globular shape, they are 

 very small, their diameter beiag only 0.0003 inch. The oiiter mem- 

 brane is echinulate, but the prominences are exceedingly minute, and 

 can only be clearly made out under a high power of the microscope. 

 I placed some spores in a drop of water on a glass slide over night, 

 protecting the latter from evaporation by a bell-glass. On the fol- 

 lowing morning the contents of many of the spores had escaped in 

 the form of colourless globular vesicles without motion, but when 

 exposed to the sun the shape of the vesicles changed, and they as- 

 sumed the form of the zoospores figured by De Bary in his PI. vii. 

 fig. 3 d d', and PI. viii. fig. 7 d, as occurring in ^thalium septicum and 

 A.rcyria punicea. 



Their size varied but little, the average length being about 0.0005 

 inch. After becoming elongated, they exhibited an active vn:'iggling 

 motion, but no motion of rotation, such as is mentioned by De Bary. 

 Their movements were confined to a very limited space ; they did 

 not travel about over the field of the microscope like the zoospores 

 of Algae. I am doubtful whether they possessed one or two ciha ; it 

 is possible the number varies. 



Sunlight and warmth appear to have a strong effect in hastening 

 the germination, for a few days after the above experiment I took 

 some spores from another specimen of Iteticularia umbrina, and 

 placed them at once in full sunshine protected as before. In very 

 little more than three hours the zoospores were produced in the 

 greatest profusion. Their number was much greater than on the 

 former occasion ; by far the greater part of them agreed exactly in 

 form and motion with those which I had previously observed. A 

 few however were of irregular ama?boid shape, similar to those shown 



