PliOTOPLASM. 5 



(6) fetrasburger* maintains tliat tlie hyaline envelope is not simply a 

 portion of the basis or ground substance of the protoplasm deprived 

 of its granules, but that it is a definite modification of it, and endowed 

 vrith various properties quite distinct from those of the ground sub- 

 stance. 



4. — Active protoplasm possesses the power of imbibing 

 water into its substance, and as a consequence, of increasing 

 its mass. This power varies with the changes in external, 

 and also in internal conditions ; many seeds, for example, 

 which do not swell up (through absorbing water) in cold 

 water, will do so when placed in that of a higher tempera- 

 ture ; but in some seeds it appears that imbibition of water 

 will not take place until after a period of rest. 



5. — When the amount of water imbibed is so great that 

 "the protoplasm may be said to be more than saturated with 

 it, the excess is separated within the protoplasmic mass in 

 the form of rounded drops, termed "Vacuoles [Vacuoli). In 

 closed cells these may become so large and abundant as to 

 be separated only by thin plates of the protoplasm (Fig. 2, 

 B). As such vacuoles become still larger, the plates are 

 broken through, and eventually we may have but one large 

 vacuole surrounded by a thin layer of protoplasm, which 

 lines the interior of the cell wall (Pig 2, C). In this way 

 ■some masses of protoplasm assume a bladder-like or vesicular 

 form, so unlike their original form that until very recently 

 their real nature has not been understood, f 'Frequently 

 when the plates which separate vacuoles break down, instead 

 of breaking entirely away they become pierced with several 

 large openings, leaving strings or bands of protoplasm which 

 extend across the cavity. * 



Occasionally, when vacuoles unite, small masses of the protoplasm 

 which previously separated them become detached as free rounded 



* " Studien iiber Protoplasma," 1876. See also Qr. Jour. Mic. Science, 

 1877, p. 134 et seq. 



f Von Mohl gave to this layer the name Primordial Utricle, and it is 

 still frequently used, but the term is objectionable, and Sachs' name of 

 Protoplasmic Sac is to be preferred. Treatment with glycerine, strong 

 alcohol, or any other substance which removes the water, will cause 

 the protoplasmic sac to contract and betome visible. 



