Apart from anthropomorphic images of Shiva, he is also represented in aniconic form of a lingam. These are depicted in various designs. One common form is the shape of a vertical rounded column in the centre of a lipped, disk-shaped object, the "yoni", symbolism for the goddess Shakti. In Shiva temples, the "linga" is typically present in its sanctum sanctorum and is the focus of votary offerings such as milk, water, flower petals, fruit, fresh leaves, and rice. According to Monier Williams and Yudit Greenberg, "linga" literally means 'mark, sign or emblem', and also refers to a "mark or sign from which the existence of something else can be reliably inferred". It implies the regenerative divine energy innate in nature, symbolized by Shiva. Some scholars, such as Wendy Doniger, view "linga" merely as an erotic phallic symbol, although this interpretation is criticized by others, including Swami Vivekananda, Sivananda Saraswati, and S. N. Balagangadhara. According to Moriz Winternitz, the "linga" in the Shiva tradition is "only a symbol of the productive and creative principle of nature as embodied in Shiva", and it has no historical trace in any obscene phallic cult.