1) By turns 2) Inturn 3) Or else 4) To and fro 
• (adv.) By alternation; when, in a proportion, the antecedent term is compared with antecedent, and consequent. • (adv.) In reciprocal succession; succeeding by turns; in alternate order.
Arranged singly at each node, as leaves on different sides of a stem.
Al·ter'nate·ly adverb 1. In reciprocal succession; succeeding by turns; in alternate order. 2. (Math.) By alternation; when, in a proportion, the antecedent term is compared with antecedent, and consequent. 
[adv] - in an alternating sequence or position
alternately 1. Happening or following in turns; succeeding each other continuously: alternate seasons of the year. 2. Designating or relating to every other one of a series: alternate lines. 3. Serving or used in place of another; substitute: an alternate plan. 4. In botany: arranged singly at each node, as leaves or buds on different sides of a ...
adverb in an alternating sequence or position; `They were deglycerolized by alternately centrifuging and mixing`; `he planted fir and pine trees alternately`