Option 1: Carl Linnaeus, a Swedish botanist, is known for his contribution to taxonomy through the development of the binomial nomenclature system. However, he did not popularize the use of embryological characters in taxonomy.

Option 2: Panchanan Maheshwari, an Indian botanist, is credited with popularizing the use of embryological characters in taxonomy. He conducted extensive research on the embryological characteristics of plants, particularly in the context of plant classification.

Option 3: Birbal Sahni was an Indian paleobotanist who made significant contributions to the field of paleobotany, studying fossil plants. However, there is no evidence to suggest that he popularized the use of embryological characters in taxonomy.

Option 4: Bentham and Hooker were botanists who collaborated on the classification of plants, resulting in the publication of "Genera Plantarum." While they made important contributions to botanical taxonomy, there is no indication that they popularized the use of embryological characters.

Therefore, option 2 - Panchanan Maheshwari - is the correct answer as he is specifically known for popularizing the use of embryological characters in taxonomy. Alert - correct answer should be Panchanan Mah