Dear Mr. Black, There is in fact already a marriage tax in Texas ["Page Two," April 23], which can kick in when both spouses have income but one is much lower than the other: Because in this community-property state most forms of income must be pooled between the spouses, the lower-earning spouse cannot benefit from income-tax relief to which he or she would in certain places be entitled if he or she were single. Unfortunately this extra taxation benefits the federal government, not Texas.