**6. Conclusions**

For vegetatively propagated species, cryopreservation has a wide applicability both in terms of species coverage, since protocols have been successfully established for root and tubers, fruit trees, ornamentals and plantation crops, both from temperate and tropical origin and in terms of numbers of genotypes/varieties within a given species. With a few exceptions, vitrification-based protocols have been employed. It is also interesting to note that in many cases, different protocols can be employed for a given species and produce comparable results. Survival is generally high to very high. Regeneration is rapid and direct, and callusing is observed only in cases where the technique is not optimized. Different reasons can be mentioned to explain these positive results. The meristematic zone of apices, from which organised growth originates, is composed of a relatively homogenous population of small, actively dividing cells, with little vacuoles and a high nucleocytoplasmic ratio. These characteristics make them more susceptible to withstand desiccation than highly vacuolated and differentiated cells. As mentioned earlier, no ice formation takes place in vitrificationbased procedures, thus avoiding the extensive damage caused by ice crystals which are formed during classical procedures. The whole meristem is generally preserved when vitrification-based techniques are employed, thus allowing direct, organised regrowth. By contrast, classical procedures often lead to destruction of large zones of the meristems, and callusing only or transitory callusing is often observed before organised regrowth starts. Other reasons for the good results obtained are linked with tissue culture protocols. Many vegetatively propagated species successfully cryopreserved until now are cultivated crops, often of great commercial importance, for which cultural practices, including *in vitro* micropropagation, are well established. In addition, *in vitro* material is "synchronized" by the tissue culture, and pregrowth procedures and relatively homogenous samples in terms of size, cellular composition, physiological state and growth response are employed for freezing, thus increasing the chances of positive and uniform response to treatments. Finally, vitrification-based procedures allow using samples of relatively large size (shoot tips of 0.5 to 2–3 mm), which can regrow directly without any difficulty. Cryopreservation techniques are now operational for large-scale experimentation in an increasing number of cases. In view of the wide range of efficient and operationally simple techniques available, any vegetatively propagated species should be amenable to cryopreservation, provided that the tissue culture protocol is sufficiently operational for this species.
