Why is the golgi apparatus said to have originated from the endoplasmic reticulum ?
The most widely accepted view is that Golgi bodies are formed from vesicles dispatched from the ER.
Transition vesicles migrate to the forming face of the Golgi body, fuse there with existing cisterna membranes, and in so doing contribute to the organelle’s growth. Presumably, a complete Golgi body can be formed in this manner.