Question

why pollen of the wrong type does not germinate on the stigma​

Answer 1

$\large\mathbf{\underline{Answer}}$

$<font color ="pink"><i>$Some pollen grains fail to germinate as they don't get all the essential conditions for the germination of pollen.

No, pollen grains of other species do not grow. ... It is so because older germinated pollens will have longer developed tube as compare to newly germinated pollen which will have shorter pollen tube.

One of these cells is a tube cell. Once the pollen grain lands on the stigma of a receptive flower (or a female cone in gymnosperms), it takes up water and germinates. Pollen germination is facilitated by hydration on the stigma, as well as by the structure and physiology of the stigma and style.
___________
$<font color ="red"><b>$$<marquee>$Thanks✊..