This is almost certainly one of Alexander’s son’s. He too is in the King’s Own Scottish Borderers and has been appointed as a Lance Corporal, which was a probationary position with no pension rights or seniority date. It was used to see how a man handled a position of authority and if he did well he would be promoted properly to the substantive and pension earning rank of Corporal, with two stripes.
The soldier shown is also a qualified 1st Class Scout, which at that time was the term used for a soldier skilled at reconnaissance and using ground to move discreetly and observe the enemy from a position of cover. This particular skill, similar to that of a Scottish ghillie or English gamekeeper was first encouraged by the then Colonel Baden Powell, who felt the need to train soldiers to have the similar abilities of a Boer farmer, having come to admire their capabilities in South Africa. He devised their qualification badge, based on a fleur-de-lis that he also later used as an insignia when forming the Boy Scout movement. The soldier is wearing a full dress doublet, with its distinctive Inverness flapped pockets on its skirts, and the Edinburgh castle collar badges of the KOSB. His headdress is the regimental glengarry cap and with his white gloves and swagger stick/cane he is dressed for walking-out of barracks, as per regulation. His waist belt is from the Slade-Wallace equipment, with its so-called ‘Union clasp’ (DIEU ET MON DROIT) and his regimental trews are from the Leslie tartan of the KOSB. I would date the photo to around 1905.