What  is to be done , suppose

 if the son is not born ?

In Hindu Dharma Sastras , it is said ,

the Putra santanam (which the son) is

deserved for all the rituals when

the elders left their mortal bodies.

Suppose, if the son is not born,

 means the Gruha Yajamani who is

the head of the family does not have son

 then his daughter’s sons are eligible

for the rituals to be done in the family.

The daughter’s son is called Dowhitrah.

But the decision and its talks  for  the

adoption of daughter’s son (Dowhitrah)

 must be made at the time daughter’s marriage.

The agreement has to be made at that time only.

So. according to the situation, and agreement

 the Gruhastu who is the head of the family,

 has to adopt that Dowhitrah who is

his daughter’s son as his own son.

After the adoption, the Dowhitra can be

deserved for doing all the rituals next to

 the gruhastu who adopted him from his daughter.

In the epic of  Mahabharatam, the Arujana

adopted his son Babhruvahan (who was born to his wife Uluchi)

 to his father-in-law who was the

father of Uluchi and did not have sons.