266 LAMARCK, HIS LIFE AND WORK 



to the reptiles, to the birds, even to the mammals, 

 and you will see, except the lacunae which are still to 

 be filled, everywhere shadings which take place be- 

 tween allied species, even the genera, and where after 

 the most industrious study we fail to establish good 

 distinctions. Does not botany, which considers the 

 other series, comprising the plants, offer us, in its 

 different parts, a state of things perfectly similar? In 

 short, what difficulties do not arise in the study and 

 in the determination of species in the genera Lichena, 

 Fucus, Carex, Poa, Piper, Euphorbia, Erica, Hiera- 

 cium, Solanum, Geranium, Mimosa, etc., etc. ? 



" When these genera were established but a small 

 number of species were known, and then it was easy 

 to distinguish them ; but at present almost all the 

 gaps between them are filled, and our specific differ- 

 ences are necessarily minute and very often insuffi- 

 cient. 



" From this state of things well established we see 

 what are the causes which have given rise to them ; 

 we see whether nature possesses the means for this, 

 and if observation has been able to give us our ex- 

 planation of it. 



" A great many facts teach us that gradually as 

 the individuals of one of our species change their 

 situation, climate, mode of life, or habits, they thus 

 receive influences which gradually change the con- 

 sistence and the proportions of their parts, their form, 

 their faculties, even their organization ; so that all of 

 them participate eventually in the changes which they 

 have undergone. 



" In the same climate, very different situations and 

 exposures at first cause simple variations in the indi- 

 viduals which are found exposed there ; but, as time 

 goes on, the continual differences of situation of in- 

 dividuals of which I have spoken, which live and suc- 

 cessively reproduce in the same circumstances, give 

 rise among them to differences which are, in some 



