STRUCTURE.] FOEMS OF BOTHRENCHYM. 59 



bundles, consisting of large tubes, lie others of a smaller 

 calibre, approaching more to the form of prosenchym. These 

 I shall distinguish, in what follows, by the name of minor 

 tubes. 



This kind of Bothrenchym may be arranged as follows : 



F. Bundles of tubes covered with bordered pits, the major 

 having smooth walls ; the minor, spiral threads between the 

 rows. Morus alba, Ulmus campestris, Clematis Vitalba. 



G. Bundles of vessels, closely pitted, with fine threads 

 between the rows of pits, Hakea oleifolia. 



H. The major tubes pitted, the minor without pits; the 

 walls of both coated inside with spiral threads. Daphne 

 Mezereum, Passerina filiformis, Bupleurum arborescens, 

 Genista canariensis. 



I. Walls of the tubes which touch other tubes pitted; 

 those which touch cells with distant pits or with none ; the 

 walls of both kinds of tubes furnished with spiral threads. 

 Samara pentandra, Tilia parvifolia, ^Esculus Hippocastanum, 

 Acer Pseudo-platanus, Cornus alba, Ilex Aquifolium, Cratsegus 

 oxyacantha, Prunus Padus, P. virginiana. 



Mohl observes, that a question may be raised as to whether 

 all these forms of pitted tissue are to be regarded as 

 bothrenchym, or those tubes only which have bordered pits 

 on all sides, the rest being regarded as "mixed vessels," 

 or whether the foregoing differences are to become the 

 foundation of more distinctions among vessels. He very 

 rightly shows that the first question only can be answered in 

 the affirmative. All these forms of tissue possess an important 

 common character in the structure of their bordered pits, by 

 which they are easily and decidedly distinguished. 



The tubes of bothrenchym exhibit here and there in their 

 length transverse dissepiments, now very distant, now close 

 together; these are either absorbed in the course of the 

 formation of the tubes, or remain pierced with a circular 

 hole, or " transverse fissures placed one above the other so as 

 to resemble the walls of a scalariform vessel." The last 

 condition is only known in partitions which have an oblique 

 position ; such fissures are analogous to the holes or gratings 



