TRANSFORMATION OF TUE GROWING-POINT INTO AN ORGAN. 465 



The cases of depression of the growing-point here mentioned constitute a few 

 examples only, which might easily be increased by hundreds of others. 



We may now return once more to the normal forms of the growing-point, and 

 to the theme which we are immediately concerned with, the formation of organs upon 

 it. Two extreme cases occur at the outset. The one consists in that the entire 

 growing-point, including its apex, is transformed into an organ — into a mass of 

 permanent tissue — where of course the growing-point as such completely gives 

 up its existence, and at the same time growth in length ceases as soon as the 

 elongation of the younger portions is concluded : such a shoot is said to have a limited 

 (definite) growth in length, in contrast to the other extreme case, where the growing- 

 point of a shoot remains persistently capable of living, and the tissue proceeding from 

 it continues to produce new axial portions and lateral organs by elongation. This may 

 be distinguished as unlimited (indefinite) 

 growth in length. As a few striking ex- 

 amples of this case the growth of the main 

 stem of Tree-ferns, Palms, Cycads, and 

 species of Adies and Finns may be ad- 

 duced; the growing-point of these plants 

 after tens or even hundreds of years is 

 still the direct prolongation of the grow- 

 ing-point of the embryo in the seed. 



We meet with proved cases of a trans- 

 formation of the entire growing-point, 

 including its apex, into an organ of de- 

 finite physiological function, and consisting 

 of permanent tissue, chiefly in the forma- 

 tion of reproductive organs at the end 

 of the shoot. Although, strictly speaking, 

 not all the foliage-shoots of Phanerogams 

 provided with so-called apical flowers be- 

 long here, there are nevertheless numerous 

 cases which are certainly to be so con- 

 sidered ; namely, all flowers with central 

 ovaries in which is developed a single central ovule, as in the Polygonese, Juglandeae, 

 Chenopodiaceae, Piperacese, and other families. In Fig. 303 the portion of the young 

 Rhubarb flower marked k k \% the nucellus of the ovule, in which arises the 

 embryo-sac with the oosphere. This portion together with the two envelopes 

 surrounding it constitute the future seed, and from microscopic investigation there 

 is no doubt that in this and similar cases the nucellus of the ovule has proceeded 

 directly from the growing-point, which had previously given rise to the carpels/", the 

 stamens a, and the floral envelopes sp. Equally without doubt is the fact in 

 question in the formation of the sexual organs of many true Mosses. Leitgeb 

 showed long ago that in the Bog-mosses {Sphag?ium) at least the first female organ 

 (archegonium) of the ' flower ' arises directly from the apical cell of the fertile shoot. 

 Kühn observed later that in the case of another Moss {Andreced) the first arche- 

 gonium arises similarly from the apical cell, and the following archegonia of the same 



[ 3 ] H h 



Fig. 302.— Development of the Fig (Ficiis Carica), 

 after Payer. 



