524 SUMMAEY OF CUBEENT BESEABCHES BELATING TO 



Development of Tissue as a Characteristic of Groups of Plants.* — 

 M. Westermaier thus sums up his conclusions on this subject. The 

 results of anatomical investigations in reference to affinity differ accord- 

 ing as the physiological idea of the subject is taken into account 

 or not. In the latter case the result is either false or uncertain, 

 while the former leads to a comparison on a rational basis. This last 

 method of inquiry results in the conclusion that in the Primulacese the 

 presence of a ring of bast may be regarded as an anatomical family 

 character. In Campanula, while one group has in the stem the 

 ordinary ring of vascular bundles with the phloem on the outer, the 

 xylem on the inner side, a second group of the genus has a phloem- 

 bundle in the pith, with or without xylem, a difference connected with 

 physiological functions. 



Stomata of Polycolymna Stuarti.f — The more or less complete 

 fusion of two or even of three stomata into one, has frequently been 

 noticed as an exceptional phenomenon. In Polycolymna Stuarti 

 (Compositse) F. Hildebrand states that it is so common, both on the 

 stem and on the leaves, that it may be regarded as a normal occur- 

 rence. 



The relative position of the two clefts in these double stomata 

 varies greatly. In some cases they are parallel, in others at right 

 angles to one another, while sometimes again one is behind the other, 

 so that only one pore belongs to the two clefts. The mode in which 

 the guard-cells are formed out of the ordinary cells of the epidermis 

 appears also to be subject to great variation. The author was un- 

 able to determine whether the cells strongly charged with protoplasm 

 divide directly into guard-cells, or whether this is only effected after 

 repeated division ; both processes appeared to take place. The 

 direction of the septum in consequence of which the guard- cells are 

 formed, is also very various ; it is sometimes vertical, sometimes 

 parallel to the wall by which the mother-cell of an epidermal cell 

 is cut off. The occurrence of double, and occasionally of treble 

 stomata, may be attributed to these numerous variations in the mode 

 of their formation. 



The stomata of Polycolymna Stuarti present also other peculiarities. 

 The guard-cells are placed in various positions as to height in 

 relation to the surrounding epidermal cells. Usually the outer walls 

 of the guard-cells are about at an equal height with those of the sur- 

 rounding cells, and this is almost invariably the case with double and 

 treble stomata. But among these are others, distributed irregularly, 

 the guard-cells of which are more or less elevated above the sur- 

 rounding epidermis, this variation being possibly connected with 

 their special function. 



The number of stomata is about the same on the under and upper 

 surfaces of the leaves ; on the under surface they are protected by 

 densely crowded glandular hairs, on the upper side by a dense felt 

 of silky hairs. The stomata with most elevated guard-cells are found 



* MB. K. Akad. Wiss. Berlin, 1881, pp. 1050-70 (1 pi.), 

 t Bot. Ceutralbl., ix. (1882) pp. 356-61 (1 pi.) 



