Chapter XIV 



155 — 



The Vacuolar System 



but only spherical vacuoles to be found at the beginning of develop- 

 ment of this type of vacuolar system. 



Among the fungi, the Saprolegniaceae constitute particularly 

 favorable objects for the study of the vacuolar system, to which we 

 will have to return later. When the mycelium of a species of Sapro- 

 legnia is examined in a solution of neutral red, there are observed 

 at the growing extremities of the plant, vacuoles which at first 

 are generally small globular elements. These elongate and appear 

 as thin, tenuous canaliculi, more or less oriented in the direction 

 of the longitudinal axis of the hypha. These canaliculi anastomose 

 and form a delicate and complicated network. In this region they 

 appear more fluid and with too little difference in refractivity be- 



FiG. 99. — Saprolegnia vitally stained with neutral red. 

 Development of the vacuolar system. 1-3, tips of growing 

 filaments; anastomosing canaliculi. 4, older filaments; fusion 

 and swelling of canaliculi. 5, later stage; precipitated bodies 

 in sap. 6, still later stage; single canal containing precipi- 

 tates. 



tween them and the cytoplasm for them to be observed without 

 staining. A little further from the tip of the hyphae, these canali- 

 culi are observed to swell, little by little, then to converge, so that 

 in differentiated regions of the hyphae, there is only a single canal 

 running from one end of the siphon to the other. This canal 

 occupies the major part of the hyphae and in it the vital dyes pro- 

 duce both numerous, semi-fluid, precipitates and diffuse staining 

 of the vacuolar sap. The cytoplasm, accordingly, now constitutes 

 only a thin layer about this canal and the nuclei are appressed to 

 the wall of the siphon. 



This vacuole, therefore, is of a special type; namely, a single 

 canal running from one end of the filament to the other and obvi- 

 ously adapted to the siphonate structure of the Saprolegniaceae. 

 This form can be found in Vaucheria but it is a rather rare type. 



