4^4 



A TEXTBOOK OF THEORETICAL BOTANY 



The phloem consists of a single ring of large sieve tubes. They are 

 very long and tapering and the pointed ends overlap. Where two sieve 



Fig. 471. — Dryopteris filix-7nas. Plants showing circinnate unfolding of leaves 



in spring of the second year. 



tubes are in contact the walls bear numerous closely arranged sieve plates, 

 which show minute adhering globules. There are no companion cells, but 



