768 REPORT—1904. 
graviperception must find some other use for them; and this will be no easy task. 
I must not omit to mention the ingenious experiments of Piccard (04), which prove 
(if they prove anything) that the root-tip is not the seat of the graviperception, 
but that this quality is found in even greater perfection in the growing region of 
the root. But until the whole of the other experimental evidence is proved to 
be illusory, I must suspend judgment on Piccard’s results and treat the question 
provisionally from our previous standpoint. 
The existence of statoliths in regions which have ceased to be capable of 
ordinary geotropic curvature is at first sight a difficulty. Thus Miss Pertz has 
found in the pith of the watercress (Nasturtium officinale) the most perfect stato- 
plasts, and this in winter, when the capacity for geotropic curvature was probably 
absent. Again, she has found movable starch in the xylem elements and in the 
cortex of a number of trees. In this case we must remember that, according to 
Meischke (99), Jost (01), and Baranetzky (01), woody branches of several years’ 
growth are capable of geotropic curvature. If so, graviperceptive organs must exist. 
We must remember, too, that in the regeneration of cuttings Voéchting (78) 
has shown that gravitation has an influence in certain cases; such cuttings must 
therefore have organs of graviperception. Or, if this is not granted as necessary, 
it seems to me conceivable that falling starch-erains, though made use of, and 
in a certain sense specialised, for graviperception, should nevertheless exist and 
serve other purposes in the economy of the plant. But this question needs further 
detailed work. 
Lastly, as part of the general question of distribution, it must be clearly pointed 
out that in a large number of plants, such as Algze and Fungi, no statoliths are 
known to exist, though their complete absence has not been proved.!’ Here we must 
either believe in Noll’s minute and hitherto unseen statoliths or in a different 
mechanism, such as hydrostatic pressure. There is no more impossibility in 
this state of things than in the presence of statoliths in Palemon and their 
absence in higher animals. And I am glad to note that both Pfeffer and Czapek 
are not disinclined to believe in the possibility of various forms of graviperception. 
Experimental Evidence. 
A flaw runs through a great part of the experimental evidence, which may be 
illustrated by an experience of my own. I found” that seedlings of Setaria and 
Sorghum could be nearly deprived of statoplasts by means of a high temperature, 
and, further, that such destarched plants were markedly less geotropic than 
normal specimens. Here seemed a proof of the theory; unfortunately, however, 
it turned out that the plants. in question were also rendered less heliotropic. 
These facts make it impossible to allow Némec’s gypsum experiment to be 
convincing. He caused a loss of starch by inclosing roots in plaster of Paris, and 
found that they had in great part lost their geotropic power. But he did not 
discover whether this loss depended on disappearance of part of the sense- 
organ or on general loss of curving power, though he has since (02) made the 
interesting observation that roots so treated are capable of hydrotropism. Again, 
Némec found in resting seeds of Vicia Faba that the statoliths are undeveloped, 
and that they appear synchronously with the power of geotroping. Would not a 
similar thing be true of the apheliotropism of Sizapis roots—z.e., might it not be 
found that they were not heliotropic until the starch appeared ? 
The same objection must be brought against Haberlandt’s otherwise con- 
vincing observation * that Zeénwm growing out of doors in late autumn or winter is 
both devoid of statoplasts and incapable of geotropism, and that the power of 
1 See Némec (Beihefte Bot. Central., B.xvii., 1904, p. 59), where he describes the 
cases and the occurrence of statoliths in the mosses and liverworts. Giesenhagen 
(01) has described heavy bodies at the tips of the rhizoids of Chara which fall to 
the physically lower side. 
2 F. Darwin (03). 
* Haberlandt (03). It seems, however, that the starchless plants had some helio- 
tropic capacity. 
