Bei der Abzählung der Samen wird jedoch, namentlich beim 2. Versuche, einige Aufmerksamkeit erfordert, da bei einzelnen Samen mancher Pflanzen die grüne Färbung des Albumens weniger entwickelt wird und anfänglich leicht übersehen werden kann.
While counting the seeds, especially in the 2nd experiment, quite some attention is demanded, however, because in individual seeds of some plants the green colouration of the albumen is less developed and can easily be overlooked in the beginning.
colouration = Färbung See p. 7, s. 6.
albumen = Albumens See p. 8, s. 3.
is less developed = weniger entwickelt wird Mendel uses the passive voice here, so a trait like the colouration of albumen is not simply a property that develops on its own but the product of developmental processes that involve the organism as a whole.
in the beginning = anfänglich The expression is a bit vague, but Mendel probably intends to say that it takes some practice to discern the green colouration.