PART II. ANATOMY AND HISTOLOGY. 



[25 



surrounds itself with a proper wall which becomes the coat of the 

 pollen-grain or of the spore. 



b. The number of the nuclei derived by repeated division from 

 the nucleus of the mother-cell before any cell-wall is formed is 

 indefinite. Each of them becomes surrounded by a portion of the 

 cytoplasm. 



FIG. 63. Zoosporangia of 'an Achlja 

 ( x 560) : A still closed ; B allowing 

 the zoospores to escape, beneath it a 

 lateral shoot c ; a the zoospores just 

 escaped ; b the abandoned membranes 

 of the zoospores which have already 

 swarmed ; e swarming zoospores. 

 (After Sachs.) 



FIG. 64. Cell-formation in the asei of Pirn 

 convorula ; af successive steps in the develop- 

 ment of the asci and spores: sh mycelium. 

 (After Sachs : x 550.) 



It is in this way that the zocspores of many Algse and Fungi are 

 formed (Fig. 63), and it is usually not until some time after their 

 escape from the mother-cell that they become clothed with a cell- 

 wall. The spores formed in the asci and sporangia of Fungi (Fig. 



