ما علاقة تساقط الاوراق في فصل الخريف لدى بعض النبات بوظيفة الوعاء الغربالي

The operation of the sieve tube stops in some plants due to the formation of callose material, leading to pore blockage and preventing nutrients from reaching the leaves, causing them to fall. The sieve tube resumes functioning in the spring after the callose material has dissolved.