Most plants do not have centrioles, so what organelle enables them to multiply?
There are many different ways to make a spindle in plant cells:
Mitotic spindles may be organized at centriolar centrosomes (only in final divisions of spermatogenesis), polar organizers (POs), plastid MTOCs, or nuclear envelope MTOCs (NE-MTOCs).
Of these, only the latter has been observed in angiosperms (flowering plants). For more info (and the source of the quote), see Brown & Lemmon, "The Pleiomorphic Plant MTOC: An Evolutionary Perspective"
Plant cells without centrioles build special vesicles from their Golgi apparatus which are important for cell division.
This website has a nice comparison of different modes of cell division. Look for "Cytokinesis by Phragmoplasts" to get to the relevant part. Phragmoplasts are not exactly a replacement for centrioles, but the whole process is a little different.
Spindle formation in plants is very different from most other eukaryotes owing to the fact that plant cells lack centrosomes or spindle pole bodies, which act as the microtubule organizing centers in animal cells. The evolutionary advantage that animal cells gain due to the presence of centrosomes is the ability to direct drastic changes in their shapes during mitosis. On the other hand, plant cells have a rigid cell wall that does not undergo any major changes in shape during mitosis; and the cell wall itself can organize many of the microtubules that form the spindle during mitosis.
Animal cells under go cell division in two phases karyo-kinesis and cyto-kinesis. During cell division (anaphase) the chromosomes are pulled away by structures called microtubule's which are formed by centrioles , just before this the centrioles line up on two opposite sides of the cell . in plant cells microtubules are made by the Golgi bodies. Animal cells are much evolved than plant cells that's why they have centrioles . Spindle formation is very much different in plant cells than in animal cells due to the absence of centrioles .