The middle portion of unspecialized mesoderm from which cartilage, bone, and blood develop is called .

The middle portion of the mesoderm that results in the formation of the connective tissues and other tissues, such as bone and cartilage is known as mesenchyme. The mesenchyme is the tissue which is composed of the loose cells embedded in the extracellular matrix composed of protein mesh and the fluid. These cells can migrate easily and thus, help in the development of the baby.

Hence, the answer is 'mesenchyme'.

chemical weathering

explanation:

evidence and logical support is essential for a scientist to do in order to maintain credibility. this is because no one can believe without any logic and without any evidence.hence a scientist can maintain credibility by proving himself and by answering logically so experiments prove very beneficial. logical hypothesis give conclusion which is acceptable. therefore, there are two main factors to maintain credibility by a scientist is evidence and logical support.