At maturity, the sieve plates become impregnated with
a)	Cellulose	b)	Pectin	c)	Suberin	d)	Callose

(d)

Sieve plates are formed by two adjoining end walls of neighbouring sieve elements of sieve tube of phloem. At maturity, these become impregnated with callose pad, which may be seasonal callose (for only limited unfavourable period) or definitive callose (formed permanently in functionless old sieve tubes).