1894. ] Comparative Histology of Pulvint. 489 
Conclusion. 
3 _From the study of the twenty-five species, I have found 
_ that there are, considering their diversity, many striking re- 
_ semblances in the external and internal anatomy of the motor 
organs, of which I here give a short summary: 
1. Organs may be found at the base of the petiole, and as 
such they are termed primary organs. In the species con- 
sidered the primary organ may be altogether absent or repre- 
sented by an imperfect development. As a general rule sim- 
ple leaves do not possess pulvini; but one exception has been 
noted in the case of Abutilon Avicenna, in which the organ 1s 
at the base of the leaf blade, or epipodium. This, however, 
I consider as a primary organ. The petiolules of each leaflet 
of pinnate and bi-pinnate leaves are transformed into motor 
organs, the secondary and tertiary organs. In the case of 
pinnate leaves, whenever any pulvini are present, it is always 
these which are found, no examples being discovered in which 
a primary organ was present without secondary organs. 
2. The organs generally show a difference in color from the 
adjacent tissue. In the organs containing chlorophyll the 
color is darker green, which it must be concluded is due to 
the fact that the organ contains but few intercellular spaces. 
The pulvini which do not contain chlorophyll are generally 
yellowish. This color is due to the presence of yellow color- 
ing matter, probably xanthophyll. In all the color may be 
Modified by trichomes, and in ‘Abutilon Avicenne there 1s a 
ted coloring matter in the epidermal pile oe 2 
3. As might be expected, different stages in the ids re 
ment of the pulvini are found in the species describe Sect 
gradations, from the very simplest indication to the per PA ane 
developed organ, are to be found. These rudimentary pulvini 
are always at the base of the petiole and never Oe as 
tertiary organs The beginning development ts to be ad a 
by the enlargement of the base of the petiole, ae ‘ 
tion of the hypodermal cells to agree with the sg 
type, and in the convergence of the schizosteles towards 
Center to form a single cylinder. 
4. The organs have a variety of for 
ae organs of the petiole, the fae wie 
erally kidney-shaped although they may © . : 
The secondary oulvint are bet? commonly roapea ae 
cross section, but different forms occur, varying from Hatte 
ms in cross section. 
eR ais pia et as rere 45 A ad iB rae ae ON a i 
