The endoplasmic reticulum (ER) without ribosomes is called smooth endoplasmic reticulum (SER). Under the microscope, it appears as a network of interconnected tubules and sacs that lack the characteristic dark granules associated with ribosomes.

Here's a more detailed description:

* Appearance: SER appears as a smooth, interconnected network of membranes, unlike the rough ER which has a rough, bumpy appearance due to the attached ribosomes.

* Shape: SER can form tubules, vesicles, and cisternae (flattened sacs). These structures are interconnected and often appear as a continuous network.

* Color: SER is typically light in color under the microscope, as it lacks the dark staining of the ribosomes.

Key Points to Remember:

* The absence of ribosomes is the defining feature of smooth ER.

* While the appearance can vary depending on the cell type and the specific staining techniques used, the general pattern of a smooth, interconnected network is characteristic of SER.

Let me know if you have any other questions about the ER!