Scott (1871) reported the parasitic nature of sandalwood plants; for many years, importance of this was not realized for good growth of trees. Barber, in 1902 examined the roots of sandalwood trees in connection with the study of spike disease and made detailed investigations on the formation and structure of haustoria’s and their mode of attachment to the root of host plant.

Haustoria on roots of sandalwood seedlings arise from external layers of rootlets, unlike lateral rootlets, which are formed deep in its tissues. If a rootlet of neighboring plant is met, sandalwood seedling grows rapidly attaching itself closely to the tootlet and develops into a mass of white tissue. It is first club-shaped but later enfolding the surface of the root attacked, it assumes the shape of a flattened bell. Usual dimensions of a fully developed haustorium are, height 3-10 mm, longer diameter 2-12 mm, shorter diameter 2-8 mm. Formation of haustoria is more or les confined to the younger roots (Fig.16).

Rama Rao (1911) from his experiments concluded that sandalwood seedlings were incapable of growing beyond one year without haustoria. He also endorsed the opinion of Barber on the selective habhit of sandalwood trees in relation to hosts.

The host parasitic combination differs from region to region the natural population.

It shows decided preference and grows best in association of certain species. The order of preference seems to be Casuarina equisitfolia, Pongamia pinnata, Albizia lebbeak, Cassia siamia, Acacia spp, Dalbergia latifolia, D.sisso etc. (Anantha-padmanabha et al. 1984).

In Australian plantations, the performance of sandalwood with Cassia siamia, Pongamia pinnata, Cathomium umbellatum and Acacia trachycarpa is very good. Swietenia mahogany tried as long term host initially did not support the growth of sandalwood. 

Mixed plantation of S.album with Dalbergia odorifera in China proved to be the best potential long term host, where as other hosts like Acacia confuse, Bischofia polycarpa and Dracontomelon duperreranum did not support good growth of sandalwood.

Sandalwood grows well with Gliricidia spp. in Sri Lanka; it is preferred because the growers can cut and sell the branches periodically. It is a very fast growing under tree.

It has been noticed that the roots of sandalwood tree had traveled a length of nearly 40 m and attacked the roots of a large Pterocarpus marsupium tree (Venkata Rao, 1938). Generally parasitic plants are smaller in size than their hosts with a single exception of sandalwood tree.

Tracer technique studies have shown that calcium could be absorbed by the roots of sandalwood seedlings, while phosphate, organic substances, amino acids, sugars and mineral phosphates were drawn from the host plant (Kunda S. Deval et al., 1974a, b).

Iyengar (1950) while studying the parasitic nature of sandalwood trees expressed that the parasite may draw only its mineral nutrients including water from host, but with green foliage it can synthesizes its own carbohohydrates like autophytes. The possibility of absorbing some organic material from host is not excluded, parasite.

Xinhua Zhang et. al (2012) has made an interesting observation on the physiology of haustorial formation. They are of the opinion that a high auxin-to-cytokinin ratio contributed to haustorial development of S.album. Numerous amount of starch in parenchyma cells around the meristamatic region above the haustorial gland and the endophyte tissue of the post-attachement haustoria were reported in Santalaceae members. Many Lysosomes were present and large-scale digestion of host cells occurred at the interface between the host and the parasite. The haustorial penetration in to the host stele was suggested to be a function of mechanical force and enzymatic activity. Analysis of the endogenous hormone levels and the structural characters in haustoria indicated that haustoria were able to synthesise phytohormones, which appeared to be necessary for cell division and differentiation during haustorial were able to synthesise phytohormones, which appeared to be necessary for cell division and differentiation during haustorial development. The authors are of the opinion that endogenous hormones are involved in the haustorial development and also transport of water and nutrients during host-parasite association.

Even when the science had not advanced much Barber (1907) was able to make a number of observations on the structure of the haustoria beginning with the formation of cushion like bodies from sandalwood roots to complete penetration inside the host roots and establishing intimate attachment between them. The haustorial connection proceeded in two stages, in the first stage, rupture and then penetration of the host root till it reached the woody portion. In the next stage, a channel communication between haustoria and vessels of the sandalwood roots is formed (Fib.17). The presence of auxin in the haustorium was reported by Srimathi and Sreenivasya (1962). Xinhua Zhang (2012) findings are an additional proof for the formation of haustoria.