VAUCHERIA 65 



continued into the tubular rootlike processes. The 

 membrane is thinly lined on its inner side with much- 

 nucleated protoplasm, and the green of the shoot por- 

 tion is due to the presence of chloroplasts arranged in a 

 netlike manner. Under favourable land conditions 

 Botrydium reproduces principally by buds which arise 

 from the green portion, put out root processes, grow to 

 full size, and become separated from the parent plant. 

 This method of increase is not well suited to aquatic 

 conditions, so if Botrydium is submerged, it meets the 

 problem of reproduction by breaking up into a number 

 of zoospores, each possessing two chloroplasts and a 

 flagellum. These zoospores drift towards, or seek out, 

 damp soil at the edge of the water, and develop into 

 normal plants; but if they cannot reach soil, in due 

 course they enter upon a resting-stage, in which they 

 remain until they find suitable conditions for germina- 

 tion. But this adaptable little plant can also meet 

 dry conditions. Lack of moisture, together with strong 

 sunlight, causes the protoplasm of Botrydium to break 

 up and the portions to round off, forming a number of 

 round cells, each invested in a cell-wall. When these 

 cells become covered with water, each one breaks up 

 into cigar- shaped gametes furnished with two flagella. 

 These gametes conjugate in pairs and form zygotes, 

 from which new plants germinate. But if the cells, 

 which break up into gametes in water, reach damp soil, 

 they at once germinate and become new plants. The 

 gamete formation, then, is an adaptation to aquatic 

 conditions. 



But within the range of the Siphonese the genus 

 Vaucheria exhibits the most remarkable sex-differentia- 



9 



