Hi Peter,
There is an Alexander Mallen in Melrose, Roxburghshire aged 25 in the 1881 census (Melrose is very close to Galashiels). He is a Gardner (domestic) and his birthplace is given as Ednam, Roxburghshire. The entry also posts a wife Marion (aged 26, b. Lauder, Berwickshire), a son James (aged 1, born Galashiels) and a daughter Eliza P. (aged 9 months, born Galashiels).
I don't see a corresponding entry in the 1891 census for a 35 year old Alexander for anywhere in Scotland, although there is a 55 year old one living in Galashiels - possibly a father?
I know this doesn't match exactly to what you posted, but it looks fairly promising. The census records from 1861 to 1901 for Scotland can be viewed at
www.scotlandspeople.gov.uk on a pay per view basis, along with birth, marriage and death certificates (actual images, not just indexes), so you should be able to track down Alexander's birth, marriage and birth of any children born in Scotland there.
Cheers,
Clare