a structural arrangement which is particularly useful in connection with solar greenhouses is provided . therein is provided a structural member in the form of a hollow bar of elongated form provided with longitudinally extending and parallel track channels having relatively narrow longitudinally extended slot mouths . a shade with a bulbous periphery is engaged in each of the track channels and a guide member is provided which changes the direction of movement of the shade as it exits from the ends of the corresponding track channels . the guide includes tubular extensions which extend into the track channels . the guide furthermore includes arcuate guide channels which are funnel shaped and operate in extension of the tubular extensions . a member operates in conjunction with the tubular extensions to a wall of the afore - mentioned bars for the mounting of the guide .