CHAPTER XII. 



GROWTH. 



By growth is usually meant an increase in the bulk of the 

 plant accompanied generally by an increase in plant sub- 

 stance. Among the lower ])lants growth is easil_y studied in 

 some of the fungi. 



240. Growth in mucor. — Some of the gonidia (often called 

 spores) may be sown in nutrient gelatine or agar, or e\en in 

 prune juice. If the culture has been placed in a warm room, in 

 the course of 24 hours, or e\'en less, the preparation will be ready 

 for study. 



241. Form of the gonidia. — It will be instructive if we first 

 examine some of the gonidia which have not been so«'n in the cul- 

 ture medium. We should note their rounded or globose form, as 

 well as their markings if they belong to one of the species with 

 spiny walls. Particularly should we note the size, and if possible 

 measure them with the micrometer, though this would not be 

 absolutely necessary for a comparison, if tlie comparison can be 

 made immediately. Now examine some of the gonidia which 

 were sown in the nutrient medium. If they ha\e not already 

 germinated we note at once that they are much larger than 

 those which iiave not been immersed in a moist medium. 



242. The gonidia absorb water and increase in size before 

 germinating. — From our study of the absor]iiion of water or 

 watery solutions of nutriment by li\-ing cells, «'e can easily un- 

 derstand the cause of this enlargement of tlic gonidium of the 

 mucor when surrounded liy the moist nutrient medium. The 

 celPsap in the spore takes u|) more water than it loses b)- diffu- 



iiS 



