Final answer:
A cross between plants of two species is known as interspecific hybridization, not inter-varietal hybridisation. Inter-varietal hybridization pertains to crossing different varieties within the same species.
Step-by-step explanation:
The statement that a cross between plants of two species is called as inter-varietal hybridisation is incorrect. Inter-varietal hybridisation refers to the mating or crossing of two different varieties of the same species, whereas a cross between two different species is known as interspecific hybridization or cross-species hybridization. When discussing the practice of creating new plants and developing novel plants through hybridization, Mendel's experiments with true-breeding pea plants are a classic example.
By crossing plants true-breeding for violet flower color with plants true-breeding for white flower color, he was able to produce hybrid offspring with predictable inheritance patterns. However, these examples of hybridization occur within the same species, making it a case of intraspecific rather than interspecific or inter-varietal hybridization.